In the proposed reconstruction method called Magnitude of Complex Filtering, a complex-valued magnetic resonance image is acquired using a flow-compensated high-resolution 3D gradient-echo sequence and the magnitude of the complex-valued image is set to 1 so that the phase information, which contains details of the local susceptibility, is emphasized. Then, the nonlinear filter of the Magnitude of Complex Filtering method is applied to the complex-valued image with a constant magnitude. This filter utilizes the magnitude of the low-pass and high-pass filtered complex data to selectively reduce the background phase effects while enhancing the local structures. The filter output is then processed to generate a susceptibility-weighted image.

Compared with the conventional susceptibility-weighted images generated by a homodyne high-pass filter, the susceptibility-weighted images from the proposed Magnitude of Complex Filtering method show significant improvement; the undesirable artifacts at the air–tissue interface regions and the brain boundaries are significantly reduced, while the contrast of the local structures of veins is enhanced.

The Magnitude of Complex Filtering method successfully reduced most background phase effects without requiring additional processing or scan time. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

We propose a two-stage frequency–space (f–x) formulation to accurately describe the dynamics of spatially-encoded magnetization under the influence of concomitant and remanence fields, which allows for correcting image distortion due to concomitant and remanence fields.

Our method is computationally efficient as it uses a combination of the fast Fourier transform algorithm and a linear equation solver. With sufficiently dense discretization in solving the linear equation, the performance of this f–x method was found to be stable among different choices of the regularization parameter and the regularization matrix.

We present this method together with numerical simulations and experimental data to demonstrate how concomitant and remanence field artifacts in ultra-low-field MRI can be corrected efficiently. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

All-inclusive bias analysis considers spatial and time-domain cross-terms for diffusion and imaging gradients. The proposed correction is based on rotation of the gradient nonlinearity tensor into the diffusion gradient frame where spatial bias of b-matrix can be approximated by its Euclidean norm. Correction efficiency of the proposed procedure is numerically evaluated for a range of model diffusion tensor anisotropies and orientations.

Spatial dependence of nonlinearity correction terms accounts for the bulk (75–95%) of ADC bias for FA = 0.3–0.9. Residual ADC non-uniformity errors are amplified for anisotropic diffusion. This approximation obviates need for full diffusion tensor measurement and diagonalization to derive a corrected ADC. Practical scenarios are outlined for implementation of the correction on clinical MRI systems.

The proposed simplified correction algorithm appears sufficient to control ADC non-uniformity errors in clinical studies using three orthogonal diffusion measurements. The most efficient reduction of ADC bias for anisotropic medium is achieved with non-lab-based diffusion gradients. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A real-time TCR (RT-TCR) algorithm is developed that only uses current and previously acquired undersampled k-space data from a 3D segmented EPI pulse sequence, with the image reconstruction done in a graphics processing unit implementation to overcome computation burden. Simulated and experimental data sets of HIFU heating are used to evaluate the performance of the RT-TCR algorithm.

The simulation studies demonstrate that the RT-TCR algorithm has subsecond reconstruction time and can accurately measure HIFU-induced temperature rises of 20°C in 15 s for 3D volumes of 16 slices (RMSE = 0.1°C), 24 slices (RMSE = 0.2°C), and 32 slices (RMSE = 0.3°C). Experimental results in ex vivo porcine muscle demonstrate that the RT-TCR approach can reconstruct temperature maps with 192 × 162 × 66 mm 3D volume coverage, 1.5 × 1.5 × 3.0 mm resolution, and 1.2-s scan time with an accuracy of ±0.5°C.

The RT-TCR algorithm offers an approach to obtaining large coverage 3D temperature maps in real-time for monitoring MR-guided high intensity focused ultrasound treatments. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

An elastic cast of a human aortic arch equipped with an 80 or 64% stenotic section was driven by a pulsatile pump. Peak velocities and peak turbulent kinetic energies of more than 3 m/s and 1000 J/m³ could be generated. Velocity vector fields and fluctuating velocities were assessed using Bayesian multipoint MR velocity encoding with varying numbers of velocity encoding points and particle tracking velocimetry in the ascending aorta.

Velocities and turbulent kinetic energies measured with 5-fold k-t undersampled 10-point MR velocity encoding and particle tracking velocimetry were found to reveal good correlation with mean differences of −4.8 ± 13.3 cm/s and r² = 0.98 for velocities and −21.8 ± 53.9 J/m³ and r² = 0.98 for turbulent kinetic energies, respectively. Three-dimensional velocity patterns of fast flow downstream of the stenoses and regions of elevated velocity fluctuations were found to agree well.

Accelerated Bayesian multipoint MR velocity encoding has been demonstrated to be accurate for assessing mean and fluctuating velocities against the reference standard particle tracking velocimetry. The MR method holds considerable potential to map velocity vector fields and turbulent kinetic energies in clinically feasible exam times of <15 min. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A field artifact removal method is introduced that is based on the sophisticated harmonic artifact reduction for phase data (SHARP) method exploiting the harmonic mean value property. The new method uses Tikhonov regularization at the deconvolution stage and is referred to as regularization enabled SHARP (RESHARP). RESHARP was compared with SHARP in a field-forward susceptibility simulation and in human brain experiments, considering effects on both field maps and the resulting susceptibility maps.

From the simulation, RESHARP was able to reduce error in the field map by 17.4% as compared with SHARP, resulting in a more accurate single-angle susceptibility map with 6.5% relative error (compared with 48.5% using SHARP). Using RESHARP in vivo, field and susceptibility maps of the brain displayed fewer artifacts particularly at the brain boundaries, and susceptibility measurements of iron-rich deep gray matter were also more consistent than SHARP across healthy subjects of similar age.

Compared with SHARP, RESHARP removes background field artifact more effectively, leading to more accurate susceptibility measurements in iron-rich deep gray matter. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Heterogeneity can confound statistical analyses. Indexed distribution analysis (IDA) transforms a reference distribution, establishing correspondences across parameter maps to which significance tests are applied.

Well-controlled simulated and clinical K^trans data from a dynamic contrast-enhanced magnetic resonance imaging study of bevacizumab were analyzed using conventional significance tests of parameter averages, histogram analysis, and IDA. Repeated pretreatment scans provided negative control; a post treatment scan provided positive control.

Histogram analysis was insensitive to simulated and known effects. Simulation: conventional analysis identified treatment effect (P ≈ 5 × 10⁻⁴) and direction, but underestimated magnitude (relative error 67–81%); IDA identified treatment effect (P = 0.001), magnitude, direction, and spatial extent (100% accuracy). Bevacizumab: conventional analysis was sensitive to treatment effect (P = 0.01; 95% confidence interval on K^trans decrease: 23–37%); IDA was sensitive to treatment effect (P < 0.05; K^trans decrease approximately 25%), inferred its spatial extent to be 94–96%, and inferred that K^trans decrease is independent of baseline value, an inference that conventional and histogram analyses cannot make.

In the presence of heterogeneity, IDA can accurately infer the magnitude, direction, and spatial extent of between samples of parametric maps, which can be visualized spatially with respect to the original parameter maps. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Based on a rough global T₁ estimator and a golden section search, T₂ is extracted from the ratio of the two echoes acquired with DESS. The new relaxometry method is evaluated from simulations and in vivo 3D measurements of the knee joint at 3T.

A pronounced reduction in the T₁-related bias of DESS-T₂ estimation and increased zonal variation in T₂ between deep and superficial cartilage layers are observed. The improvement becomes particularly evident in the range of low flip angles (α < 45°), commonly used for morphological DESS imaging.

Using a simple global T₁ estimate, the reliability of DESS-T₂ quantification can be considerably increased. The results emphasize the potential of DESS to fuse accurate quantitative T₂ and morphological imaging of the musculoskeletal system within one single scan. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The CEST effect of porcine blood samples was investigated on a 3.0 T MRI scanner using various power levels and on a 14.1 T NMR spectrometer. As a proof-of-concept that CEST can be used to image blood in vivo, the technique was applied in two locations of healthy human volunteers, namely, the femoral artery and the M1-segment of the middle cerebral artery.

The blood sample experiments showed that maximum CEST Magnetization Transfer Ratio asymmetry (MTR_asym) values of ∼ 12% were achieved, with likely contributions from multiple blood components. These findings were confirmed during the in vivo experiments where CEST signal of blood was clearly greater than surrounding muscular (2%) and brain tissue (3%).

Ex vivo and in vivo results show that blood is a suitable CEST agent that generates sufficient CEST contrast relative to surrounding tissue.

Ten patients with moderate to severe chronic obstructive pulmonary disease were scanned with a 3D single breath-hold pO₂ mapping sequence.

Images showed signal increasing over time in some lung regions due to delayed ventilation during breath-hold. Regions of physically unrealistic negative pO₂ values were seen in all patients, and regional mean pO₂ values of −0.3 bar were measured in the two patients most affected by delayed ventilation (where mean time to signal onset was 3–4 s).

Movement of gas within the lungs during breath-hold causes regional changes in signal over time that are not related to oxygen concentration, leading to erroneous pO₂ measurements using the linear oxygen-dependent signal decay model. These spatio-temporal sources of signal change cannot be reliably separated at present, making pO₂ mapping using this methodology unreliable in chronic obstructive pulmonary disease patients with significant bullous emphysema or delayed ventilation. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

GL261 and 4C8 glioma cells labeled with iron oxide particles or with a fluorescent probe were injected into the brains of syngeneic mice and allowed to develop into ∼10-mm³ tumors. Texture analysis was used to quantitatively describe and compare the label distribution patterns in the two tumor types.

The label was seen to remain predominantly in the tumor core in GL261 tumors, but become more randomly distributed throughout the tumor volume in 4C8 tumors. Histologically, GL261 tumors displayed a more invasive, aggressive phenotype, although the distribution of mitotic cells in the two tumors was similar.

The redistribution of a cellular label during tumor growth is characteristic of a tumor model. The label distribution map reflects more than simple differences in cell proliferation and is likely influenced by differences in the tumor microenvironment. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The 9L tumor-bearing rats (n = 8) and fresh chicken eggs (n = 4) were scanned on a 4.7-T animal magnetic resonance imaging scanner. Z-spectra over an offset range of ±6 ppm were acquired with different saturation powers, followed by the magnetization transfer-ratio asymmetry analyses around the water resonance.

The nuclear Overhauser enhancement signal upfield from the water resonance (−2.5 to −5 ppm) was clearly visible at lower saturation powers (e.g., 0.6 µT) and was larger in the contralateral normal brain tissue than in the tumor. Conversely, the APT effect downfield from the water resonance was maximized at relatively higher saturation powers (e.g., 2.1 µT) and was larger in the tumor than in the contralateral normal brain tissue. The nuclear Overhauser enhancement decreased the APT-weighted image signal, based on the magnetization transfer-ratio asymmetry analysis, but increased the APT-weighted image contrast between the tumor and contralateral normal brain tissue.

The APT and nuclear Overhauser enhancement image signals in tumor are maximized at different saturation powers. The saturation power of roughly 2 μT is ideal for APT-weighted imaging at clinical B₀ field strengths. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

We intended to track endogenous neuroblast migration from the subventricular zone to the stroke area using previously described methods for in vivo labeling of endogenous neuroblasts with MPIOs and following migration with high resolution MRI.

MPIOs accumulation in stroke regions of endothelin-1-treated brains involves two dynamic steps: an initial rapid cell independent mechanism, followed by slower MPIOs accumulation. While the latter may in part be attributable to cell dependent delivery of the particles, the cell independent mechanism complicates the interpretation of the data. Strategies aimed at prelabeling the stem cell niche reduced cell independent MPIOs accumulation, but failed to abolish it.

We conclude that MRI-based neural stem/progenitor cell tracking via direct injection of MPIOs into the lateral and third ventricles, requires significant validation in models of brain disease/trauma. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Twenty-eight patients were examined using DCE-MRI pre-, post-one cycle, and just prior to surgery. The semiquantitative parameters included longest dimension, tumor volume, initial area under the curve, and signal enhancement ratio related parameters, while quantitative parameters included K^trans, v_e, k_ep, v_p, and τ_i estimated using the standard Tofts-Kety, extended Tofts-Kety, and fast exchange regime models.

Our preliminary results indicated that the signal enhancement ratio washout volume and k_ep were significantly different between pathologic complete responders from nonresponders (P < 0.05) after a single cycle of chemotherapy. Receiver operator characteristic analysis showed that the AUC of the signal enhancement ratio washout volume was 0.75, and the AUCs of k_ep estimated by three models were 0.78, 0.76, and 0.73, respectively.

In summary, the signal enhancement ratio washout volume and k_ep appear to predict breast cancer response after one cycle of neoadjuvant chemotherapy. This observation should be confirmed with additional prospective studies. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Two high permittivity dielectric pads on the anterior and posterior sides of the thorax were numerically designed and implemented using an aqueous suspension of barium titanate. The effects on the average transmit efficiency, B₁ homogeneity, reception sensitivity, and contrast-to-noise ratio were verified in vivo on a dual-transmit system with the body coil driven in conventional quadrature and radiofrequency-shimmed mode.

Statistically significant improvements in average transmit efficiency, B₁ homogeneity, and contrast-to-noise ratio were measured in healthy volunteers (n = 11) with body mass indices between 20.3 and 34.9. Simulations show that no radiofrequency hot spots are introduced by the dielectric material.

High permittivity pads are shown to reduce specific absorption rate, improve B₁ homogeneity, and increase contrast-to-noise ratio in functional cardiac magnetic resonance at 3 T. The results presented in this work show that the current approach is more effective than dual-channel radiofrequency shimming. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A new pulse sequence, dubbed as spatially encoded localized COSY (SLCOSY), based on spatially encoded technique, was developed for localized 2D correlated spectroscopy. It can be used to collect a full 2D spectrum in a single scan and thus on a subsecond timescale.

SLCOSY spectrum of a two-compartment phantom was obtained with a total acquisition time of 773 ms, with its volume localization confirmed. Localized 2D COSY spectrum of a proton magnetic resonance spectroscopy brain phantom within 12 s shows the ability of SLCOSY to detect the metabolites at physiological concentrations. All 10 constituent metabolites in this phantom are reliably detected. SLCOSY spectrum of a sample of pig brain tissue with the acquisition time of 32 s demonstrates the feasibility of SLCOSY for the detection of biological tissues. Twelve pairs of cross peaks are identified.

The new method proposed herein enables ultrafast collection of a full 2D COSY spectrum, and it can also be used for fast in vivo analysis of metabolites, when signal-to-noise ratio is not a limiting factor. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

mapping was performed in 81 healthy subjects in seven centers using different 3 T systems. was calculated from a dual-echo gradient echo sequence and was assessed in several deep gray matter structures. The inter-scanner and inter-subject variability of was calculated by means of the coefficient of variation before and after correcting for age.

Significant center effects were seen in some regions which get lost after age correction. The coefficient of variation for the inter-center variability was much lower (<5.6%) than for the intra-subject variability (6.7%–11.7%). in the putamen and red nucleus scaled with cortical volume while in the globus pallidus and the substantia nigra was negatively associated with white matter volume.

is a robust and reproducible measure in a multicenter setting provided that a standardized MRI protocol is used. The relationship between iron concentration in deep gray matter and volume of specific brain compartments needs further investigation. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

In this study, a phantom for the investigation of PVEs and their influence on diffusion parameters in fine structures of different diameter is presented. The phantom is produced by winding wet polyester fibers onto a spindle. The resulting fiber strands have well defined square cross-sections of 1–25 mm² and provide a homogeneous and high fractional anisotropy (FA ≈ 0.9).

Several PVEs are demonstrated and analyzed. It is shown that inferred results such as the fiber geometry and diffusion parameters strongly depend on the relative position of the structure of interest to the voxel-grid. Several implications of PVEs on post-processing methods such as Tract-based Spatial Statistics and fiber tractography are demonstrated.

These results show that the handling of PVEs in common post-processing tasks can be problematic, and that the presented phantom provides a valuable tool for the improvement and evaluation of these effects. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Six-echo gradient echo imaging and single-voxel MRS measurements were performed on the proximal femur of seven healthy volunteers. The bone marrow fat spectrum was characterized based on the magnitude of measurable fat peaks and an a priori knowledge of the chemical structure of triglycerides, in order to accurately extract the water peak from the overlapping broad fat peaks in MRS. The imaging-based fat fraction results were then compared to the MRS-based results both without and with taking into consideration the presence of short water components in MRS.

There was a significant underestimation of the fat fraction using the MRS model not accounting for short species with respect to the imaging-based fat fraction. A good equivalency was observed between the fat fraction using the MRS model accounting for short species and the imaging-based fat fraction (R² = 0.87).

The consideration of the short water species effect on bone marrow fat quantification is essential when comparing MRS-based and imaging-based fat fraction results. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

dualMRI was translated from high-field research systems to a 3T clinical system. Precision was calculated using repeated tests of a silicone phantom. dualMRI was demonstrated by visualizing displacements and strains in an intervertebral disc and compared to T₂ measured during cyclic loading.

The displacement and strain precisions were 24 µm and 0.3% strain, respectively, under the imaging parameters used in this study. Displacements and strains were measured within the intervertebral disc, but no correlations were found with the T₂ values.

The translation of dualMRI to a 3T system unveils the potential for in vivo studies in a myriad of tissue and organ systems. Because of the importance of mechanical behavior to the function of a variety of tissues, it's expected that dualMRI implemented on a clinical system will be a powerful tool in assessing the interlinked roles of structure, mechanics, and function in both healthy and diseased tissues. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

In this work, aVLV measurements were performed in rats using hyperpolarized ¹²⁹Xe MRI and compared with hyperpolarized ³He measurements of aVLV under matched ventilation conditions. Whole-lung compliance was also determined. Partial volume, apparent diffusion coefficient, and effective transverse relaxation time corrections were applied during postprocessing to reduce bias between methods.

Mean apparent diffusion coefficient of the trachea was 0.83 ± 0.09 cm²/s and 0.067 ± 0.011 cm²/s for ³He and ¹²⁹Xe, respectively. Mean apparent diffusion coefficient of parenchyma was 0.21 ± 0.07 cm²/s and 0.027 ± 0.008 cm²/s for ³He and ¹²⁹Xe, respectively. Mean transverse relaxation time values were 1.57 ± 0.25 ms and 2.80 ± 0.25 ms for ³He and ¹²⁹Xe, respectively, in a model trachea and 3.18 ± 1.00 ms and 4.88 ± 0.60 ms for ³He and ¹²⁹Xe, respectively, for lung parenchyma. Mean aVLV values were 7.07 ± 0.67 mL and 6.99 ± 1.00 mL at 14 cmH₂O and 4.88 ± 0.71 mL and 5.36 ± 0.76 mL at 10 cmH₂O obtained with ³He and ¹²⁹Xe, respectively, demonstrating good agreement between ¹²⁹Xe and ³He.

¹²⁹Xe offers an important alternative to ³He for hyperpolarized gas MRI of aVLV in rats. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A theoretical analysis shows: (1) The correlations in k-space are encoded in the null space of a calibration matrix. (2) Both approaches restrict the solution to a subspace spanned by the sensitivities. (3) The sensitivities appear as the main eigenvector of a reconstruction operator computed from the null space. The basic assumptions and the quality of the sensitivity maps are evaluated in experimental examples. The appearance of additional eigenvectors motivates an extended SENSE reconstruction with multiple maps, which is compared to existing methods.

The existence of a null space and the high quality of the extracted sensitivities are confirmed. The extended reconstruction combines all advantages of SENSE with robustness to certain errors similar to GRAPPA.

In this article the gap between both approaches is finally bridged. A new autocalibration technique combines the benefits of both. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A novel preparation pre-pulse, called saturation pulse prepared heart-rate-independent inversion recovery, is introduced, which consists of a combination of saturation and inversion pulses to remove the magnetization history in each heartbeat in late gadolinium enhancement (LGE) imaging and eliminate the need for rest periods in T₁ mapping. The proposed LGE and T₁ mapping sequences were evaluated against conventional LGE and modified Look-Locker inversion sequences using numerical simulations, phantom and imaging in healthy subjects and patients with suspected or known cardiovascular disease.

Simulations and phantom experiments show that the saturation pulse prepared heart-rate-independent inversion recovery pre-pulse in LGE reduces ghosting artifacts and results in perfect nulling of the healthy myocardium in the presence of arrhythmia. In T₁ mapping, saturation pulse prepared heart-rate-independent inversion recovery results in (a) reduced scan time (17 vs. 9 heartbeats), (b) insensitivity to heart rate for long T₁, and (c) increased signal homogeneity for short T₁. LGE images in a patient in atrial fibrillation during the scan show improved myocardial nulling. In vivo T₁ maps demonstrate increased signal homogeneity in blood pools and myocardium.

The proposed sequences are insensitive to heart rate variability, yield improved LGE images in the presence of arrhythmias, as well as T₁ mapping with shorter scan times. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A dependency between k-space coverage and local resolvability of the image causes k-space samples to have a spatially localized contribution to the reconstruction of the spin density. On the basis of this observation, a concept for alias-free data undersampling is developed, which is referred to as the local field of view concept.

On the basis of this concept, a fast sampling trajectory is developed. It is evaluated with simulations and experiments (both using a phantom and in vivo) for MRI with, as an example, pure quadrupolar encoding fields. To demonstrate that the concept is only applicable to (spatially) nonlinear encoding, a comparison with linear encoding is provided.

Application of the local field of view concept results in a localized adaptation of the image resolution by undersampling higher frequency k-space samples without introducing aliasing.

A new effect of nonlinear spatial encoding magnetic fields was found, which allows more efficient data sampling and at the same time counterbalancing the natural variation in image resolution. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

We used iron oxide for MR imaging and a cyanide dye approved by the Food and Drug Administration (indocyanine green) for optical imaging and estimated the in vivo detection of transplanted pancreatic islets.

The poly(lactic-co-glycolic acid) nanoparticles were associated with the islets in vitro and were successfully detected by 4.7 T (MR) and optical imaging, without other toxic effects. When labeled islets were transplanted under the mouse kidney capsule, in vivo T₂/ -weighted scans with 4.7 T MR detected as few as 300 labeled islets by 4 weeks. Optical in vivo imaging revealed indocyanine green fluorescence by 2 and 4 days after transplantation of islets containing 250 and 500 µg/mL poly(lactic-co-glycolic acid) nanoparticles, respectively. These results were further supported by the immunohistochemical results for insulin and iron in the recipient mouse kidney and pancreas.

Taken together, these data indicate that poly(lactic-co-glycolic acid) nanoparticles may be used to label transplanted islets and may be imaged with in vivo MR and optical imaging systems. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

CEST agents that were responsive and unresponsive to the activity of urokinase plasminogen activator were shown to have negligible interaction with each other. A CEST-fast imaging with steady state precession (FISP) MRI protocol was used to acquire MR CEST spectroscopic images with a Capan-2 pancreatic tumor model after intravenous injection of the CEST agents. A function of (super)-Lorentzian line shapes was fit to CEST spectra of a region-of-interest that represented the tumor.

The CEST effects from each agent showed the same initial uptake into tumor tissues, indicating that both agents had the same pharmacokinetic transport rates. Starting 5 min after injection, CEST from the enzyme-responsive agent disappeared more quickly than CEST from the unresponsive agent, indicating that the enzyme responsive agent was being catalyzed by urokinase plasminogen activator, while both agents also experienced net pharmacokinetic washout from the tumor.

CatalyCEST MRI demonstrates that dynamic tracking of enzyme-responsive and unresponsive CEST agents during the same in vivo MRI study is feasible. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Using a 16-channel B₁⁺ shimming system, we compare different dynamically applied B₁⁺ phase shimming approaches on the radiofrequency excitation to improve contrast homogeneity for a (0.5 mm)³ resolution multislab TOF acquisition. In addition, B₁⁺ shimming applied on the venous saturation pulse was investigated to improve venous suppression, subcutaneous fat signal reduction and enhanced background suppression originating from MT effect.

B₁⁺ excitation homogeneity was improved by a factor 2.2–2.6 on average depending on the shimming approach, compared to a standard CP-like phase setting, leading to improved vessel conspicuity particularly in the periphery. Stronger saturation, higher fat suppression and improved background suppression were observed when dynamically applying B₁⁺ shimming on the venous saturation pulse.

B₁+ shimming can significantly improve high resolution TOF vascular investigations at ultrahigh field, holding strong promise for non contrast-enhanced clinical applications. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The Generalized Lorentzian Approach suggests that the local contribution to frequency shifts in white matter does not depend on the average tissue magnetic susceptibility (as suggested by Lorentzian sphere approximation), but on the distribution and symmetry of magnetic susceptibility inclusions at the cellular level. We use ex vivo rat optic nerve as a model system of highly organized cellular structure containing longitudinally arranged myelin and neurofilaments. The nerve's cylindrical shape allowed accurate measurement of its magnetic susceptibility and local frequency shifts.

We found that the volume magnetic susceptibility difference between nerve and water is −0.116 ppm, and the magnetic susceptibilities of longitudinal components are −0.043 ppm in fresh nerve, and −0.020 ppm in fixed nerve.

The frequency shift observed in the optic nerve as a representative of white matter is consistent with generalized Lorentzian approach but inconsistent with Lorentzian sphere approximation. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Variable FA bSSFP cardiac cine imaging was achieved using an asynchronous k-space acquisition, which is asynchronous to the cardiac cycle (aVFA-bSSFP). Bloch simulations and phantom experiments were performed to compare the signal, resolution, and frequency response of the variable FA bSSFP and CFA-bSSFP schemes. Ten volunteers were imaged with different aVFA-bSSFP and asynchronous CFA-bSSFP schemes and compared to conventional segmented CFA-bSSFP.

The SAR of aVFA-bSSFP is significantly decreased by 36% compared to asynchronous CFA-bSSFP (1.9 ± 0.2 vs. 3.0 ± 0.2 W/kg, P <  10⁻¹⁰) for similar blood-myocardium CNR (34 ± 6 vs. 35 ± 9, P = 0.5). Alternately, the CNR of the aVFA-bSSFP is improved by 28% compared to asynchronous CFA-bSSFP (49 ± 9 vs. 38 ± 8, P <  10⁻⁴) with similar SAR (3.2 ± 0.5 vs. 3.3 ± 0.5 W/kg, P = 0.6).

aVFA-bSSFP can be used for lower SAR or higher contrast cardiac cine imaging compared to the conventional segmented CFA-bSSFP imaging. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

This concept uses a single coil array rather than separate arrays for parallel excitation/reception and B₀ shimming. It relies on a novel design that allows a radiofrequency current (for excitation/reception) and a direct current (for B₀ shimming) to coexist independently in the same coil.

Proof-of-concept B₀ shimming experiments were performed with a two-coil array in a phantom, whereas B₀ shimming simulations were performed with a 48-coil array in the human brain.

Our experiments show that individually optimized direct currents applied in each coil can reduce the B₀ root-mean-square error by 62–81% and minimize distortions in echo-planar images. The simulations show that dynamic shimming with the 48-coil iPRES array can reduce the B₀ root-mean-square error in the prefrontal and temporal regions by 66–79% as compared with static second-order spherical harmonic shimming and by 12–23% as compared with dynamic shimming with a 48-coil conventional shim array.

Our results demonstrate the feasibility of the iPRES concept to perform parallel excitation/reception and B₀ shimming with a unified coil system as well as its promise for in vivo applications. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The Hahn spin echo formed by the first two 90° radiofrequency pulses is balanced to consecutively acquire two additional images with different echo times and generate an inherent field map, while the diffusion-prepared stimulated echo signal remains unaffected. For every diffusion-encoding direction, an intrinsically registered field map is estimated dynamically and used to effectively and inherently correct for off-resonance artifacts in the reconstruction of the corresponding diffusion-weighted image.

After correction with the dynamically acquired field maps, local blurring artifacts are specifically removed from individual stimulated echo diffusion-weighted images and the estimated diffusion tensors have significantly improved spatial accuracy and larger fractional anisotropy.

Combined with the self-navigated interleaved spirals acquisition scheme, our new method provides an integrated high-resolution short-echo time diffusion tensor imaging solution with inherent and dynamic correction for both motion-induced phase errors and off-resonance effects. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Ultrashort echo time pulse sequences were used to study six bovine and nine human bone samples at 1.5 T and 3 T using single- and bi-component analysis.

On average, the bound water of bovine bone decreased by 16% (from 0.32 ms at 1.5 T to 0.27 ms at 3 T, P < 0.01) and the bound water of human bone decreased by 21% (from 0.42 ms at 1.5 T to 0.33 ms at 3 T, P < 0.01) at the higher field strength. The free water of bovine bone decreased by 50% (from 4.23 ms at 1.5 T to 2.12 ms at 3 T, P < 0.001) and the free water of human bone decreased by 68% (from 7.65 ms at 1.5 T to 2.46 ms at 3 T, P < 0.001) at the higher field strength. Bound and free water fractions showed only minor change with field strength in bovine (< 2%, P > 0.05) and human bone (< 4%, P > 0.05).

Ultrashort echo time bi-component analysis provides consistent bound and free water fractions at 1.5 T and 3 T, thereby allowing field-independent comparisons. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The design of acquisition in multishell is still an open and active field of research, however. In this work, we provide a general method to design multishell acquisition with uniform angular coverage. This method is based on a generalization of electrostatic repulsion to multishell.

We evaluate the impact of our method using simulations, on the angular resolution in one and two bundles of fiber configurations. Compared to more commonly used radial sampling, we show that our method improves the angular resolution, as well as fiber crossing discrimination.

We propose a novel method to design sampling schemes with optimal angular coverage and show the positive impact on angular resolution in diffusion MRI. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A 3D multiecho gradient-echo sequence was used. Phase evolution during the multiecho was used to produce quantitative susceptibility maps, while the phase value at zero echo time was retrieved, and used to generates quantitative conductivity maps. Electromagnetic simulations were performed to evaluate the phase distribution due to conductivity variations. Phantom and in vivo data were also acquired to assess the quality of images produced.

Simulations demonstrated that phase differences across objects increases with size and conductivity. For an accurate conductivity estimate, the maximum echo time was approximately equal to the true value in order to achieve signal-to-noise ratio maximization. The most accurate susceptibility was obtained when separating phase contribution from conductivity. Phantom and in vivo results showed good quality images representing the electromagnetic properties.

A simultaneous quantitative electromagnetic property imaging approach is demonstrated here. The approach not only improves the efficiency of mapping electromagnetic properties, but can also improve the accuracy of susceptibility mapping by separating image phases introduced by conductivity and susceptibility. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A 3D Cartesian spoiled gradient echo technique was adapted to enable the use of a variable echo time approach in combination with a highly asymmetric readout. T₂* was calculated monoexponentially and biexponentially using three- and five-parametric non-linear fits, respectively.

From a total of 68 evaluated menisci, 48 were normal, 12 were degenerated, and eight had tears. Mean values for the short (T₂*_s) and long (T₂*_l) T₂* components were as follows: in normal menisci, 0.82 ± 0.38/15.0 ± 5.4 ms, respectively; in degenerated menisci, 1.29 ± 0.53/19.97 ± 5.59 ms, respectively; and, in meniscal tears, 2.05 ± 0.73 and 26.83 ± 7.72 ms, respectively. Biexponentially fitted T₂* demonstrated a greater ability to distinguish normal and degenerated menisci using receiver operating characteristic (ROC) analysis (higher area under curve as well as higher specificity and sensitivity).

This study suggests that biexponential fitting, used for T₂* calculation in the menisci, provides better results compared to monoexponential fitting. Observed changes in T₂* result from the matrix reorganization in degenerative processes in the menisci, which affects the collagen fiber orientation, as well as content. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Navigator-gated three-dimensional late gadolinium enhancement acquisitions were performed in 18 patients using tracking end-expiratory accept/reject (EE-ARA) and CLAWS algorithms in random order.

Retrospective analysis of the stored navigator data shows that CLAWS scan times are very close to (within 1%) or equal to the fastest achievable scan times while EE-ARA significantly extends the acquisition duration (P < 0.0001). EE-ARA acquisitions are 26% longer than CLAWS acquisitions (378 ± 104 s compared to 301 ± 85 s, P = 0.002). Image quality scores for CLAWS and EE-ARA acquisitions are not significantly different (4.1 ± 0.6 compared to 4.3 ± 0.6, P = ns). Numerical phantom simulations show that the non-uniform k-space ordering introduced by CLAWS results in slight, but not statistically significant, reductions in both blood signal-to-noise ratio (10%) and blood-myocardium contrast-to-noise ratio (12%).

CLAWS results in markedly reduced acquisition durations compared to EE-ARA without significant detriment to the image quality. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Computer simulations were performed to examine the accuracy of the proposed method and to find the optimal off-resonance irradiation pulse duration (T_irad) and power level (ω₁). Our approach, with echo planar imaging data acquisition, was applied to animals at 9.4 T and humans at 3 T with ω₁/2π = 100 Hz and 177 Hz, respectively. Steady-state MT ratio and relaxation rate were obtained from a pair of MT images at a T_irad, with and without inversion.

For T_irad ≥ 0.4 s, steady-state MT ratio, and relaxation rate measured at any single T_irad agreed well with those of the conventional fitting method that uses multiple T_irad. Our simulation indicates that a higher ω₁ can use a shorter Tirad.

Steady-state MT ratio and relaxation rate can be determined from MT data with only one, short T_irad by incorporation of an inversion prepulse. This MT imaging approach is simple, fast, and easily implementable. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Three pairs of adiabatic pulses were employed for voxel localization in J-resolved LASER and two pairs in J-resolved semi-LASER. The first half of t₁ period was inserted between the last pair of adiabatic pulses, which was proposed in this work to obtain two-dimensional adiabatic J-resolved spectra of human brain for the first time. Phantom and human experiments were performed to demonstrate their feasibility and advantages over conventional J-resolved spectroscopy (JPRESS).

Compared to JPRESS, J-resolved LASER or J-resolved semi-LASER exhibited significant suppression of chemical shift artifacts and additional J-refocused peaks from spatially dependent J-coupling evolution, and demonstrated insensitivity to the change of RF frequency offset over large bandwidth.

Experiments on phantoms and human brains verified the feasibility and strengths of two-dimensional adiabatic J-resolved spectroscopy at 3T. This technique is expected to advance the application of in vivo two-dimensional MR spectroscopy at 3T and higher field strengths for more reliable and accurate quantification of metabolites. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The protocol requires acquisition of 13 standard diffusion-weighted images, followed by linear combination of log diffusion signals, thus avoiding nonlinear optimization. The method was evaluated on an ex vivo rat brain and an in vivo human brain. Parameter maps were compared with MK estimated from a standard diffusion kurtosis imaging (DKI) data set comprising 160 diffusion-weighted images.

The new MK displays remarkably similar contrast to MK, and the proposed protocol acquires the necessary data in less than 1 min for full human brain coverage, with a postprocessing time of a few seconds. Scan–rescan reproducibility was comparable with MK.

The framework offers a robust and rapid method for estimating MK, with a protocol easily adapted on commercial scanners, as it requires only minimal modification of standard diffusion-weighting protocols. These properties make the method feasible in practically any clinical setting. Magn Reson Med 000:000–000, 2013. © 2013 Wiley Periodicals, Inc.

The system was constructed including transmission lines to reduce radiofrequency induction and switching circuits to remove induced voltages. Adaptive filters, trained by 12-lead measurements outside MRI and in two orientations inside MRI, were used to remove magneto-hydro-dynamic voltage. The system was tested on 10 (one exercising) volunteers and four arrhythmia patients.

Switching circuits removed most imaging-induced voltages (residual noise <3% of the R-wave). Magneto-hydro-dynamic voltage removal provided intra-MRI ECGs that varied by <3.8% from those outside the MRI, preserving the true S-wave to T-wave segment. In premature ventricular contraction (PVC) patients, clean ECGs separated premature ventricular contraction and sinus rhythm beats. Measured heating was <1.5°C. The system reliably acquired multiphase (steady-state free precession) wall-motion-cine and phase-contrast-cine scans, including subjects in whom 4-lead gating failed. The system required a minimum repetition time of 4 ms to allow robust ECG processing.

High-fidelity intra-MRI 12-lead ECG is possible. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

An MRI-compatible VDT system was constructed by modifying a commercial system. Hardware was added to reduce MRI gradient-ramp and radiofrequency unblanking pulse interference. VDT patches and cables were modified to reduce heating. Five swine cardiac VDT electro-anatomic mapping interventions were performed, navigating inside and thereafter outside the MRI.

Three-catheter VDT interventions were performed at >12 frames per second both inside and outside the MRI scanner with <3 mm error. Catheters were followed on VDT- and MRI-derived maps. Simultaneous VDT and imaging was possible in repetition time >32 ms sequences with <0.5 mm errors, and <5% MRI signal-to-noise ratio (SNR) loss. At shorter repetition times, only intracardiac electrocardiogram was reliable. Radiofrequency heating was <1.5°C.

An MRI-compatible VDT system is feasible. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A new method is proposed for denoising diffusion-weighted magnitude images. The proposed method formulates the denoising problem as an maximum a posteriori} estimation problem based on Rician/noncentral χ likelihood models, incorporating an edge prior and a low-rank model. The resulting optimization problem is solved efficiently using a half-quadratic method with an alternating minimization scheme.

The performance of the proposed method has been validated using simulated and experimental data. Diffusion-weighted images and noisy data were simulated based on the diffusion tensor imaging model and Rician/noncentral χ distributions. The simulation study (with known gold standard) shows substantial improvements in single-to-noise ratio and diffusion tensor estimation after denoising. In vivo diffusion imaging data at different b-values were acquired. Based on the experimental data, qualitative improvement in image quality and quantitative improvement in diffusion tensor estimation were demonstrated. Additionally, the proposed method is shown to outperform one of the state-of-the-art nonlocal means-based denoising algorithms, both qualitatively and quantitatively.

The single-to-noise ratio of diffusion-weighted images can be effectively improved with rank and edge constraints, resulting in an improvement in diffusion parameter estimation accuracy.

The method, T₂-Relaxation-Under-Phase-Contrast MRI, utilizes complex subtraction of phase-contrast to isolate pure blood signal, applies nonslice-selective T₂-preparation to measure T₂, and converts T₂ to oxygenation using a calibration plot.

Following feasibility demonstration, several technical aspects were examined, including validation with an established global Y_v technique, test–retest reproducibility, sensitivity to detect oxygenation changes due to hypoxia and caffeine challenges, applicability of echo-planar-imaging (EPI) acquisition to shorten scan duration, and ability to study veins with a caliber of 1–2 mm.

T₂-Relaxation-Under-Phase-Contrast was able to simultaneously measure Y_v in all major veins in the brain, including sagittal sinus, straight sinus, great vein, and internal cerebral vein. T₂-Relaxation-Under-Phase-Contrast results showed an excellent agreement with the reference technique, high sensitivity to oxygenation changes, and test–retest variability of 3.5 ± 1.0%. The use of segmented-EPI was able to reduce the scan duration to 1.5 minutes. It was also feasible to study pial veins and deep veins.

T₂-Relaxation-Under-Phase-Contrast MRI is a promising technique for vessel-specific oxygenation measurement. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Poly(lactide-co-glycolide) (PLGA) encapsulated magnetic nano and microparticles were fabricated. Multiple biologically relevant experiments were performed to assess cell viability, cellular performance, and stem cell differentiation. In vivo MRI experiments were performed to separately test cell transplantation and cell migration paradigms, as well as in vivo biodegradation.

Highly magnetic nano (∼100 nm) and microparticles (∼1–2 µm) were fabricated. Magnetic cell labeling in culture occurred rapidly achieving 3–50 pg Fe/cell at 3 h for different particles types, and >100 pg Fe/cell after 10 h, without the requirement of a transfection agent, and with no effect on cell viability. The capability of magnetically labeled mesenchymal or neural stem cells to differentiate down multiple lineages, or for magnetically labeled immune cells to release cytokines following stimulation, was uncompromised. An in vivo biodegradation study revealed that NPs degraded ∼80% over the course of 12 weeks. MRI detected as few as 10 magnetically labeled cells, transplanted into the brains of rats. Also, these particles enabled the in vivo monitoring of endogenous neural progenitor cell migration in rat brains over 2 weeks.

The robust MRI properties and benign safety profile of these particles make them promising candidates for clinical translation for MRI-based cell tracking. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

FAIR and pCASL were compared in terms of sensitivity, absolute quantification, reproducibility and flexibility of implementation. Multislice and coronal imaging were also investigated. Studies were performed at 11.75 T with volumic transmitter/receiver radiofrequency coils and fast imaging.

pCASL demonstrated better experimental flexibility and higher sensitivity compared to FAIR (> +20%). Renal blood flow values in the range of 550–750 mL/100 g/min for the cortex and of 140–230 mL/100 g/min for the medulla, consistent with literature data, were measured.

pCASL was successfully applied at very high field for mouse renal blood flow measurements, demonstrating high sensitivity, flexibility and multislice imaging capability. pCASL may be considered as a method of choice for mouse kidney perfusion studies. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Multiple long-axis slices rotated around the center axis of the left ventricle are acquired using a 2D Golden Radial acquisition scheme. This sampling approach allows for both real-time data and retrospectively reordered cine images with different temporal resolutions. Functional information from the left ventricle is used for retrospective reordering of the data to reconstruct cine images without an external ECG signal. Afterward, individual 2D cine slices are synchronized using physiological information on the mitral valve closure. The proposed approach was assessed in 15 volunteers and applied in four patients for feasibility.

Physiological gating signals obtained with our approach show great correlation with an ECG reference signal. Functional parameters determined with the presented method show a relative difference of less than 1.3% when compared with an ECG-gated approach.

It is successfully demonstrated that functional assessment of the heart is possible using physiological information obtained directly from MR image data. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

There are two aspects to improve the reconstruction quality. One is that spatial correlation among slices is used by extending the atoms in dictionary learning from patches to blocks. The other is that the dictionary-learning scheme is used at two resolution levels; i.e., a low-resolution dictionary is used for sparse coding and a high-resolution dictionary is used for image updating. Numerical experiments are carried out on in vivo 3D MR images of brains and abdomens with a variety of undersampling schemes and ratios.

The proposed method (dual-DLMRI) achieves better reconstruction quality than conventional reconstruction methods, with the peak signal-to-noise ratio being 7 dB higher. The advantages of the dual dictionaries are obvious compared with the single dictionary. Parameter variations ranging from 50% to 200% only bias the image quality within 15% in terms of the peak signal-to-noise ratio.

Dual-DLMRI effectively uses the a priori information in the dual-dictionary scheme and provides dramatically improved reconstruction quality.

The k-t SENSE method allows dynamic imaging at high acceleration factors with high reconstruction quality. However, the low resolution training data required by k-t SENSE may cause undesired temporal filtering effects in the reconstructed images.

In this work, a feedback regularization approach is applied to realize auto-calibration of the k-t SENSE algorithm. To that end, a full resolution training data set is calculated from the accelerated data itself using a TSENSE reconstruction. The reconstructed training data are then fed back for the actual k-t SENSE reconstruction. For evaluation of our approach, temporal filtering effects are quantified by calculating the modulation transfer function and noise measurements are done by Monte-Carlo simulations.

Computer simulations and cardiac imaging experiments demonstrate an improved temporal fidelity of auto-calibrated k-t SENSE compared to standard k-t SENSE.

Auto-calibrated k-t SENSE provides high quality reconstructions for dynamic imaging applications. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

With this aim, optimal control theory was applied to create pulses that for near-equivalent spins accomplish transfers in and out of the singlet state with maximum efficiency while ensuring robustness toward variations in the nuclear spin system Hamiltonian (chemical shift, J-couplings, B₁ and B₀ magnetic field inhomogeneity).

The pulses are designed to accomplish efficient transfer with low B₁ amplitude, essential for applications on preclinical and clinical MR scanners.

It is demonstrated that significantly improved efficiency and robustness can be obtained within the limitations of typical MR scanner performance.

A new method is introduced to simultaneously quantify T₁ and T₂ within one single scan based on a triple echo steady-state (TESS) approach in combination with an iterative golden section search. TESS relaxometry is optimized and evaluated from simulations, in vitro studies, and in vivo experiments.

It is found that relaxometry with TESS is not biased by T₂/T₁, insensitive to B₀ heterogeneities, and, surprisingly, that TESS-T₂ is not affected by B₁ field errors. Consequently, excellent correspondence between TESS and reference spin echo data is observed for T₂ in vitro at 1.5 T and in vivo at 3 T.

TESS offers rapid T₁ and T₂ quantification within one single scan, and in particular B₁-insensitive T₂ estimation. As a result, the new proposed method is of high interest for fast and reliable high-resolution T₂ mapping, especially of the musculoskeletal system at high to ultra-high fields. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Echo planar images were obtained using a non-Cartesian density weighted k-space trajectory. In contrast to linear Cartesian acquisition, distortions arising in non-Cartesian acquisitions can only be corrected using conjugate phase-based methods. Up to now these methods require a time consuming field map acquisition in undistorted coordinates. In this work, a phase-labeled reference EPI scan was performed in a very short time, yielding a displacement map in distorted coordinates. Subsequently, this map was applied to itself and thus transformed into undistorted coordinates. The echo planar images were then corrected with a frequency-segmented conjugate phase method. The results were compared with corrections based on a multi-echo reference field map acquired in undistorted coordinates.

Uncorrected density weighted EPI exhibited geometric distortions and severe ringing artifacts. These distortions could be successfully corrected using the novel method. The quality was comparable to corrections based on the multi-echo reference field map. The novel method shortens the field map acquisition duration by a factor of 64.

The method presented allows correcting non-Cartesian EPI from a reference scan consisting of only two phase-labeled echo planar images. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

In this study, we quantified the ability to detect osteoarthritis (OA) severity in human cartilage explants using a multicontrast magnetic resonance imaging (MRI) approach, inclusive of novel displacements under applied loading by MRI, relaxivity measures, and standard MRI.

Displacements under applied loading by MRI measures, which characterized the spatial micromechanical environment by 2D finite and Von Mises strains, were strong predictors of histologically assessed OA severity, both before and after controlling for factors, e.g., patient, joint region, and morphology. Relaxivity measures, sensitive to local macromolecular weight and composition, including T_1ρ, but not T₁ or T₂, were predictors of OA severity. A combined multicontrast approach that exploited spatial variations in tissue biomechanics and extracellular matrix structure yielded the strongest relationships to OA severity.

Our results indicate that combining multiple MRI-based biomarkers has high potential for the noninvasive measurement of OA severity and the evaluation of potential therapeutic agents used in the treatment of early OA in animal and human trials. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

C57BL/6-mice were inoculated with B16-F10 cells. CEST–MR images of tumor and bladder were acquired upon the i.v. administration of Yb-HPDO3A (1.2 mmol/Kg). pH was assessed by the use of a ratiometric method.

Yb-HPDO3A distributes well in the extracellular space of the tumor allowing the detection of good levels of saturation transfer (ST). It is excreted throughout kidneys and accumulated in the bladder thus yielding a strong CEST signal from urine. By comparing the ST% obtained upon selective irradiation of the two OH resonances belonging to the two isomeric forms of Yb-HPDO3A, it has been possible to measure the extracellular pH for each voxel (0.22 mm³). The obtained pH-maps of tumors show a great heterogeneity. Marked differences are associated to tumor staging.

The application of Yb-HPDO3A to measure extracellular tumor pH provides a good spatio-temporal resolution and it does not require the prior knowledge of the contrast agent concentration. The herein reported data support the potential clinical translation of Yb-HPDO3A. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A time-resolved three-dimensional radial acquisition with iterative sensitivity-encoding reconstruction images the entire abdomen and thorax with high spatial and temporal resolution, using real-time three-dimensional fluoroscopy to match the breath hold to contrast arrival. The sequence was tested on 17 subjects, including eight patients with HCC or other hypervascular focal lesions.

This technique was successful in acquiring volumetric imaging of the entire liver with 2.1-mm isotropic spatial and true 4-s temporal resolution.

This technique may be suitable for detecting, characterizing, and monitoring the treatment of HCC. It also holds significant potential for perfusion modeling, which may provide a noninvasive means to rapidly determine the efficacy of chemotherapeutic agents in these tumors over the entire liver volume. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Parallel magnetic resonance imaging reconstruction problem can be formulated as a multichannel sampling problem where solutions are sought analytically. However, the channel functions given by the coil sensitivities in parallel imaging are not known exactly and the estimation error usually leads to artifacts. In this study, we propose a new reconstruction algorithm, termed Sparse BLind Iterative Parallel, for blind iterative parallel imaging reconstruction using compressed sensing. The proposed algorithm reconstructs both the sensitivity functions and the image simultaneously from undersampled data. It enforces the sparseness constraint in the image as done in compressed sensing, but is different from compressed sensing in that the sensing matrix is unknown and additional constraint is enforced on the sensitivities as well. Both phantom and in vivo imaging experiments were carried out with retrospective undersampling to evaluate the performance of the proposed method.

Experiments show improvement in Sparse BLind Iterative Parallel reconstruction when compared with Sparse SENSE, JSENSE, IRGN-TV, and L₁-SPIRiT reconstructions with the same number of measurements.

The proposed Sparse BLind Iterative Parallel algorithm reduces the reconstruction errors when compared to the state-of-the-art parallel imaging methods. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

This approach requires a minor modification of a conventional stack-of-spirals sequence and analyzes data collected on three overlapping orthogonal cylinders.

Initial results are presented for acquired and synthesized phantom data and in vivo data.

The proposed method includes gradient coupling effects, requires no phantom measurements or specialized hardware, is robust to off-resonance effects, and estimates independent continuous delays for each gradient channel over the data-sampling period. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

In diffusion-weighted MRI studies of neural tissue, the classical model assumes the statistical mechanics of Brownian motion and predicts a monoexponential signal decay. However, there have been numerous reports of signal decays that are not monoexponential, particularly in the white matter.

We modeled diffusion in neural tissue from the perspective of the continuous time random walk. The characteristic diffusion decay is represented by the Mittag-Leffler function, which relaxes a priori assumptions about the governing statistics. We then used entropy as a measure of the anomalous features for the characteristic function.

Diffusion-weighted MRI experiments were performed on a fixed rat brain using an imaging spectrometer at 17.6 T with b-values arrayed up to 25,000 s/mm². Additionally, we examined the impact of varying either the gradient strength, q, or mixing time, Δ, on the observed diffusion dynamics.

In white and gray matter regions, the Mittag-Leffler and entropy parameters demonstrated new information regarding subdiffusion and produced different image contrast from that of the classical diffusion coefficient. The choice of weighting on q and Δ produced different image contrast within the regions of interest.

We propose these parameters have the potential as biomarkers for morphology in neural tissue. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Computer simulations were completed demonstrating the potential of this approach. Wire patterns were produced using the boundary element method to remove magnetic field inhomogeneities over multiple regions of interest. Field maps and regions of interest histograms were compared with and without the shim present. A prototype was constructed confirming the feasibility of this approach within the magnetic resonance environment. Metal–oxide–semiconductor field-effect transistors were used. Two field maps were acquired with the prototype producing gradient and offset field profiles, respectively. The experimental field profiles were compared with simulation.

The wire patterns significantly increased field homogeneity over all regions of interest investigated. The field profiles produced by the prototype matched simulation. No imaging artifacts were produced.

An approach to control the shape of a current distribution over a single surface has been described. This method has the potential to improve field homogeneity over any desired region of interest and is particularly well suited for dynamic applications. The method is feasible with current technology and construction techniques. Magn Reson Med 000:000–000, 2013. © 2013 Wiley Periodicals, Inc.

We propose a novel Poisson ellipsoid sampling scheme and enforce multiple spatial and temporal l₁-norm constraints during image reconstruction. Retrospective and prospective analyses were performed to validate the approach.

Retrospectively, no mean bias or diverging trend was observed as the acceleration rate was increased from 3× to 18×; less than 10% error was measured in K^trans at any individual rates in this range. Prospectively accelerated images at a rate of 36× enabled full brain coverage with 0.94 × 0.94 × 1.9 mm³ spatial and 4.1 s temporal resolutions. Images showed no visible degradation and provided accurate K^trans values when compared to a clinical population.

Highly accelerated dynamic MRI using compressed sensing and parallel imaging provides accurate permeability modeling and enables full brain, high resolution acquisitions. Magn Reson Med 000:000–000, 2013. © 2013 Wiley Periodicals, Inc.

The proposed navigator is incorporated into a real-time interactive software that allows rapid setup and efficient motion extraction, and runs on standard clinical hardware without any additional dedicated components for processing. The proposed 2D cardiac fat image navigator was compared with the conventional 1D diaphragm navigator in free-breathing b-SSFP coronary MRAs in 12 healthy volunteers at 1.5T.

Real-time motion extraction from 2D cardiac fat navigator images was feasible within 20 ms, enabling successful prospectively gated coronary magnetic resonance angiographies in all subjects. Compared to 1D diaphragmatic navigator, 2D fat image navigator reduced scan time by 38% (P < 0.0005), and significantly improved vessel sharpness, myocardial suppression, and image quality (P < 0.05).

This demonstrates the feasibility of a 3D SSFP coronary magnetic resonance angiography sequence using a 2D epicardial fat image as a navigator for real-time prospective motion tracking. Magn Reson Med 000:000–000, 2013. © 2013 Wiley Periodicals, Inc.

Fully sampled DTI datasets were obtained from both simulated phantom and experimental heart sample, with diffusion gradient applied in six directions. The k-space data were undersampled retrospectively with acceleration factors from 2 to 6. Diffusion-weighted images were reconstructed by solving an l₂-l₁ norm minimization problem. Reconstruction performance with varied signal-to-noise ratio and acceleration factors were evaluated by root-mean-square error and maps of reconstructed DTI indices.

Superiority of distributed compressed sensing over basic compressed sensing was confirmed with simulation, and the reconstruction accuracy was influenced by signal-to-noise ratio and acceleration factors. Experimental results demonstrate that DTI indices including fractional anisotropy, mean diffusivities, and orientation of primary eigenvector can be obtained with high accuracy at acceleration factors up to 4.

Distributed compressed sensing is shown to be able to accelerate DTI and may be used to reduce DTI acquisition time practically.

Spatiotemporal encoding concepts lead to a spatially selective, chemical-shift-dependent echo, with simultaneous dephasing of all other off-resonant species. The approach only requires applying a pair of suitable radiofrequency-swept pulses, and allows arbitrary shaping of the spatial profiles.

Based on arguments derived for chirp pulses operating in the sequential-sweep approximation, quadratic-phase SLR excitation and refocusing waveforms were designed and used to collect 2D slice- and shift-selective images on a 7 T microimaging system (phantoms). The same strategy was used to obtain multi-slice echo-planar and spin-echo images of breast on human volunteers in a 3 T scanner.

The method managed to deliver excellent shift-selective multi-slice images in phantoms and human volunteers. Simultaneous water and fat images were also collected in a single, interleaved acquisition mode on both platforms, using straightforward sequence and reconstruction modifications of the basic scheme.

A new way to achieve chemical shift selectivity with high quality spatial profiling is achieved, without the usual requirements for playing out fast oscillating gradients in conjunction with carefully timed radiofrequency pulses. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

To minimize line shape distortions and spectral leakage artifacts in MR spectroscopic imaging (MRSI).

A spatially and spectrally regularized non-Cartesian MRSI algorithm that uses the line shape distortion priors, estimated from water reference data, to deconvolve the spectra is introduced. Sparse spectral regularization is used to minimize noise amplification associated with deconvolution. A spiral MRSI sequence that heavily oversamples the central k-space regions is used to acquire the MRSI data. The spatial regularization term uses the spatial supports of brain and extracranial fat regions to recover the metabolite spectra and nuisance signals at two different resolutions. Specifically, the nuisance signals are recovered at the maximum resolution to minimize spectral leakage, while the point spread functions of metabolites are controlled to obtain acceptable signal-to-noise ratio.

The comparisons of the algorithm against Tikhonov regularized reconstructions demonstrates considerably reduced line-shape distortions and improved metabolite maps.

The proposed sparsity constrained spectral deconvolution scheme is effective in minimizing the line-shape distortions. The dual resolution reconstruction scheme is capable of minimizing spectral leakage artifacts. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A 16-element dual-row transmit array and a 31-element receive array were developed. Based on an accurate numerical model of the transmit array, the deposited power was calculated for different head sizes and positions. The influence of the receive array on the transmit field was characterized. Parallel imaging performance and signal-to-noise ratio of the receive array were evaluated.

On average, a two fold increase in signal-to-noise ratio was observed in the whole-brain volume when compared with a 16-channel elliptic microstrip transceiver array. The benefits of combining the two arrays, B₁⁺ shimming in three directions and high receive sensitivity, are demonstrated with high-resolution in vivo images.

The dual-row transmit array provides whole-brain coverage at 9.4 T, which, in combination with the helmet-shaped receive array, is a valuable radio frequency configuration for ultra-high field magnetic resonance imaging of the human brain. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The proposed method is based on constrained centroidal Voronoi tessellations of the upper hemisphere with a novel pseudometric.

The time complexity of the proposed tessellations was shown to be effectively linear, i.e., on the order of the number of sampling measurements. For small sample size, the proposed method was comparable with the state-of-the-art method (a direct iterative minimization of the electrostatic potential energy of a collection of electrons antipodal-symmetrically distributed on the unit sphere) in terms of the sampling uniformity. For large sample size, in which the state-of-the-art method is infeasible, the reconstructed images from the proposed method has less streak and ringing artifacts, when compared with those of the commonly used methods.

This work proposed a unique and optimal approach to solving a long-standing problem in generating uniform sampling points for three-dimensional radial MRI. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

In separate scans at 1.5 T, a hip prosthesis phantom and a sphere filled with gadolinium solution were imaged with SR-FPE and compared to conventional three-dimensional-fast spin-echo. Spectral modeling was performed on the SR-FPE data to generate the following parametric maps: species-specific signal (ρ_species), B₀ field inhomogeneity, and R*₂. The prosthesis phantom was also scanned using a 16-channel coil at 1.5 T. The fully sampled k-space data were retrospectively undersampled to demonstrate the feasibility of parallel imaging acceleration in all three phase-encoding directions, in combination with corner-cutting and half-Fourier sampling. Finally, SR-FPE was performed with an acetone/water/oil phantom to test chemical species separation.

High quality distortion-free images and parametric maps were generated from SR-FPE. A 4 h SR-FPE scan was retrospectively accelerated to 12 min while preserving spectral information and 7.5 min without preserving spectral data. Chemical species separation was demonstrated in the acetone/water/oil phantom.

This work demonstrates the feasibility of SR-FPE to perform chemical species separation and spectrally resolved imaging near metal without distortion, in scan times appropriate for the clinical setting. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A multishell sampling scheme was optimized using the electrostatic repulsion algorithm, combined with optimal ordering. The optimal protocol, using as few measurements as possible, was determined through leave-n-out analyses. Parsimonious model selection criteria were used to select between nested models, comprising up to three restricted compartments. The schemes were evaluated using both through Monte-Carlo simulations and in vivo data.

The optimization/model selection procedure resulted in increased accuracy and precision on the estimated parameters, allowing for a reduction in acquisition time and marked improvements in data quality. The final protocol provided whole brain coverage data in only 12 min.

Through careful optimization of the acquisition and analysis pipeline for the composite hindered and restricted model of diffusion, it is possible to reduce acquisition time for whole brain datasets to a time that is clinically applicable. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A temporally well-controlled visual stimulation paradigm with a known neuronal firing pattern in monkey visual cortex provides a means of detecting and testing the magnitude of the neuronal current-induced attenuation in neuronal current magnetic resonance imaging.

Placing a series of acquisition windows to fully cover the entire response duration enables a thorough detection of any detectable MR signal attenuation induced by the stimulus-evoked neuronal currents.

No significant neuronal current-induced MR signal attenuation was observed in the putative V1 in any participated subjects.

The present magnetic resonance imaging technique is not sensitive enough to detect neuronal current-induced MR signal attenuation, and the upper limit of this attenuation was found to be less than 0.07% under the study condition. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A uniform sampling distribution was derived for spinning gradient EPRI acquisition (uniform spinning sampling, USS) and compared to the existing (equilinear spinning sampling, ESS) acquisition strategy. Novel corrections were introduced to reduce artifacts in experimental data.

Simulations demonstrated that USS puts an equal number of projections near each axis whereas ESS puts excessive projections at one axis, wasting acquisition time. Artifact corrections added to the magnetic gradient waveforms reduced noise and correlation between projections. USS images had higher SNR (85.9 ± 0.8 vs. 56.2 ± 0.8) and lower mean-squared error than ESS images. The quality of the USS images did not vary with the magnetic gradient orientation, in contrast to ESS images. The quality of rat heart images was improved using USS compared to that with ESS or traditional fast-scan acquisitions.

A novel EPRI acquisition which combines spinning gradient acquisition with a uniform sampling distribution was developed. This USS spinning gradient acquisition offers superior SNR and reduced artifacts compared to prior methods enabling potential improvements in speed and quality of EPR imaging in biological applications. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The proposed enhancements were achieved by flexible organization of prior knowledge, configurations for different situations, the inclusion of measured macromolecular baseline contribution, additional baseline splines and a model-free lineshape based on self-deconvolution. The new software was tested and tuned on simulated data and subsequently applied to in vivo intrasubject and intersubject data.

Fit results of simulated and acquired spectra show good overall quality suggesting the potential reliable detection of up to 18 metabolites on a 3T system yielding Cramer-Lower-Bounds below 20%.

The proposed enhanced version of ProFit together with two-dimensional J-resolved spectroscopy offers the opportunity to reliably detect a wide selection of important brain metabolites on 3T. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Multi-slice data were acquired at 3 T using a novel inversion recovery echo planar imaging (IR-EPI) pulse sequence with varying contrast weightings and an efficient rotating slice acquisition order, at rest and during visual activation. A biophysical model was used to estimate absolute cerebral blood volume at rest and during activation, and oxygenation during activation, on data from 13 normal human subjects.

Cerebral blood volume increased by 21.7% from 6.6 ± 0.8 mL/100 mL of brain parenchyma at rest to 8.0 ± 1.3 mL/100 mL of brain parenchyma in the occipital cortex during visual activation, with average blood oxygenation of 84 ± 2.1% during activation, comparing well with literature.

The method is feasible, and could foster improved understanding of the fundamental physiological relationship between neuronal activity, hemodynamic changes, and metabolism underlying brain activation; complement existing methods for estimating compartmental changes; and potentially find utility in evaluating vascular health. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The approach presented here embeds EPR pulses within a balanced steady state free precession sequence. Unlike other Overhauser-enhanced MRI methods, no separate Overhauser prepolarization step is required. This steady-state approach also eliminates the problem of time-varying Overhauser-enhanced signal and provides constant polarization in the sample during the acquisition. A further increase in temporal resolution was achieved by incorporating undersampled k-space strategies and compressed sensing reconstruction.

We demonstrate 1 × 2 × 3.5 mm³ resolution at 6.5 mT across a 54 × 54 × 110 mm³ sample in 33 s while sampling 30% of k-space.

The work presented here overcomes the main limitations of Overhauser enhanced MRI as previously described in the literature, drastically improving speed and resolution, and enabling new opportunities for the measurement of free radicals in living organisms, and for the study of dynamic processes such as metabolism and flow. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Acquisition times for chemical shift based water–fat separation imaging are lengthy, and many applications rely on image acceleration techniques. In this study, we present an integrated compressed sensing, parallel imaging, corrected water–fat separation technique for water–fat imaging of highly accelerated acquisitions. Reconstruction times are reduced using coil compression.

The proposed technique is demonstrated using a customized IDEAL-SPGR pulse sequence to acquire retrospectively and prospectively undersampled datasets of the liver, calf, knee, and abdominal cavity. This technique is shown to offer comparable image quality relative to fully sampled reference images for a range of acceleration factors. At high acceleration factors, this technique is shown to offer improved image quality over parallel imaging.

A technique is described that uses compressed sensing and parallel imaging to reconstruct -corrected water and fat images from accelerated datasets. Acceleration factors as high as 7.0 are shown with excellent image quality. These high acceleration factors enable water–fat separation with higher resolution or greater anatomical coverage in breath-hold applications. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The phantom was designed to represent an artery flanked on both sides by vein. Both arterial and venous components have different temporal dynamics but are confluent, which corresponds to a difficult scenario for HYPR. Spatial and temporal fidelity was investigated by measuring signal intensity profiles through the phantom both orthogonal to as well as along the direction of motion.

Spatial fidelity profiles measured from the HYPR processed images yielded full-width-at-half-maximum values very similar to those measured in non-HYPR-processed images. Furthermore, there was no significant spreading of the motion phantom leading edge in HYPR processed images.

Although HYPR processing has certain characteristic artifacts that are discussed, the technique can be used to improve image quality of highly undersampled time frame images with minimal loss of spatial or temporal fidelity. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The ethical committee waived the need for informed consent to measure 17 patients with high grade prostate cancer on a 3T system. A semi-LASER sequence was used with an echo time of 144 ms and optimized interpulse timing for a spectral citrate shape with high signal intensity. An LCModel basis set was developed for fitting choline, creatine, spermine, citrate, and lactate and was used to fit all spectra in tumor-containing voxels. For patients without detectable lactate, the minimal detectable lactate concentration was determined by adding in all spectra of tumor tissue a simulated lactate signal. The amplitude of the simulated lactate signal was iteratively decreased until its fit reached a Cramér Rao lower bound >20%, which was then set as the patient-specific detection limit.

In none of the patients a convincing lactate signal was found. We estimated that on average the lactate levels in high grade prostate cancer are below 1.5 mM (range 0.9–3.5 mM), Interestingly, in one patient with extensive necrosis in the tumor biopsy samples (Gleason score 5+5), large lipid resonances were observed, which originated from the tumor.

The minimal detectable lactate concentration of 1.5 mM in high grade prostate cancer indicates that if lactate is increased it remains at low concentrations. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The regional differentiation of the arterial spin labeling water between the glomerular capsular space and the renal parenchyma was characterized and measured according to their MR relaxation properties (T_1ρ or T₂), and applied to the estimation of filtration fraction and single-kidney GFR. The proposed approach was tested to quantify GFR in healthy volunteers at baseline and after a protein-loading challenge.

Biexponential decay of the cortical arterial spin labeling water MR signal was observed. The major component decays the same as parenchyma water; the minor component decays much slower as expected from glomerular ultra-filtrates. The mean single-kidney GFR was estimated to be 49 ± 9 mL/min at baseline and increased by 28% after a protein-loading challenge.

We developed an arterial spin labeling-based MR imaging method that allows us to estimate renal filtration fraction and singe-kidney GFR without use of exogenous contrast. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The FLEX sequence measures modulation of the water signal based on the chemical shift evolution of solute proton magnetization as a function of evolution time. Time-domain analysis of this water signal allows identification of different solute components and provides a mechanism to separate out the rapidly decaying MTC components with short effective transverse relaxation time ( ) values.

FLEX imaging of paraCEST agents was possible in vitro in phantoms and in vivo in mouse kidneys and bladder. The results demonstrated that FLEX is capable of separating out the MTC signal from tissues in vivo while providing a quantitative exchange rate for the rapidly exchanging paraCEST water protons by fitting the FLEX time-domain signal to FLEX theory.

The first in vivo FLEX images of a paraCEST agent were acquired, which allowed separation of the tissue MTC components. These results show that FLEX imaging has potential for imaging the distribution of functional paraCEST agents in biological tissues. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

T₁ relaxograms from normal human brain were computed by a spatially regularized inverse Laplace transform after estimating the apparent inversion efficiency.

With sufficiently long inversion-time sampling (ca. 5 × T₁ of cerebrospinal fluid), the T₁ relaxogram revealed a short-T₁ peak (106–225 ms). The apparent fraction of this water component increased in human brain white matter from 8.3% at 3 T, to 11.3% at 4 T and 15.0% at 7 T. The T₂* of the short-T₁ peak at 3 T was shorter, 27.9 ± 13.0 ms, than that of the long-T₁ peak, 51.3 ± 5.6 ms.

The short-T₁ fraction is interpreted as the water resident in myelin. Its detection is facilitated by longer T₁ of axoplasmic water at higher magnetic field. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A novel 3D localized 2D ZQC method is presented. The combination of cardiac/respiratory triggering and post-acquisition navigator echo correction provides high-quality 2D NMR spectra in vivo.

The lipid profile of the human breast could be quantified by 2D ZQC NMR in 100% of the subjects despite a wide range of magnetic field homogeneity. With conventional 1D ¹H MRS, the magnetic field homogeneity was only adequate in 60% of the subjects. The results from 2D ZQC NMR and 1D NMR are in good correspondence, both in vitro and in vivo.

It has been demonstrated that high quality and quantitative 2D ZQC NMR spectra can be acquired from human breast tissue at 7 T. While the simplicity and sensitivity of 1D MRS are preferable when the magnetic field homogeneity is adequate, the 2D ZQC method provides a viable alternative in cases where this requirement cannot be met. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The institutional-review-board approved study consisted of 48 segmental small-bowel motility-plots out of a previous study with 25 patients (15 men/10 women; mean 39 years, standard deviation ± 14.67) undergoing MRI (1.5 T, GE-Medical Systems; two-dimensional-Fiesta, pulse repetition time 2.91, echo time 1.25, flip-angle 45°, matrix 256 × 256, slice thickness 10 mm) were evaluated. Calculations of contraction frequency was performed either manually or using Lomb-Scargle-periodograms and Sinus-Fitting method. The results were compared using intraclass correlation coefficient, Friedman's-test and Wilcoxon-matched-paired-signed-rank-test (P < 0.05 considered statistically significant).

Mean contraction frequency was 5.69 (standard deviation ± 1.99) for manual calculations showing moderate interreader reliability (intraclass correlation coefficient 0.72; 95% confidence-interval: 0.59;0.82). No significant difference (P = 0.776) was found to Lomb-Scargle-periodograms (5.34 contractions-per-minute [cpm], standard deviation ± 2.47; P = 0.174) and to the sinus-fitting-method (5.47 cpm; standard deviation ± 2.57; P = 0.0779). For the latter calculations failed in 3/48 plots, while manual and Lomb-Scargle-periodograms could be performed successfully in all 48/48 plots.

Herein, we could show that Lomb-Scargle-periodograms and Sinus-Fitting are fast and reliable methods to automatically measure small-bowel contraction frequencies even in noisy small bowel motility plots. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Transmit pulses are created by an offline computer equipped with a Pentek excitation card (PCIe model 78621) that was built around the Texas Instruments D/A converter (DAC5688).

The spectral purity of pulses made in this way surpasses the quality of pulses made by the standard modulators of the scanner, even when using the same pulse-creation algorithm. There is no need to mix reference waveforms with the magnetic resonance imaging signal to obtain inter-k-space coherency for different repetitions. The key was the use of a system clock to create the Larmor frequency used for pulse formation. The 3- and 4-fold slice accelerations were tested using phantoms as well as functional and resting-state magnetic resonance imaging of the human brain.

Synthesizers with limited modulation-time steps should be replaced not only because of the improved spectral quality of radiofrequency pulses but also for the exceptional coherence of pulses at different slice-selection frequencies. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Multislice SPEN employing either inversion or stimulated echo pulses and timed to fulfill the demands of full refocusing, are demonstrated. The performance of the ensuing methods was examined in “Hybrid” modalities encoding data in k- and direct-space, in low-specific absorption rate stimulated-echo approaches, and in direct-space SPEN approaches.

When applied in phantoms and in in vivo systems, the ensuing single-shot sequences evidenced similar robustness, sensitivity, and resolution qualities as previously discussed 2D single-slice schemes, while enabling a rapid sampling of the third dimension via multislicing.

The unique benefits deriving from fully refocused, multislice, single-scan SPEN sequences were corroborated by phantom tests, as well as by in vivo scans at 3 and 7 T. Low specific absorption rate multislice SPEN variants compatible with human studies were demonstrated. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Reproducible non-linear phase components are calibrated using 2D-EPI navigators and tailored RF excitation pulses designed. Real time correction of rigid-body motion was not yet implemented.

Phase correction was confirmed with full signal DW-FSE images obtained on co-operative subjects. Full diffusion tensor acquisitions were obtained and color-coded maps displaying principal fiber directionality calculated. Results were consistent with corresponding EPI acquisitions except for absence of spatial distortions.

Combining the proposed method with real time compensation of rigid-body motion has the potential to allow high quality, distortion free diffusion imaging throughout the brain. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

We modified the accelerated 3D Look-Locker T₁ measurement technique to allow rapid measurement of flip angle. By removing the inversion pulses and interleaving two radio frequency pulses with different amplitude, it is possible to fit directly for the true flip angle using a reduced number of parameters. This technique, non-inverted Double Angle Look-Locker, allows quick and efficient mapping of the flip angle in 3D.

non-inverted Double Angle Look-Locker is validated in vitro against the actual flip angle imaging technique for a range of flip angles and T₁ values. Flip angle maps produced with non-inverted Double Angle Look-Locker can be acquired in approximately 1 min, and are accurate to within 10% of the actual flip angle imaging measurement. It is shown to accurately measure the excited slab profile of several different pulses. An application to correcting in vivo DESPOT T₁ data is presented.

The presented technique is a rapid method for mapping flip angles across a 3D volume, capable of producing a flip angle map in approximately 1 min. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Respiratory motion makes hepatic ablation using high intensity focused ultrasound (HIFO) challenging. Previous HIFU liver treatment had required apnea induced during general anesthesia. We describe and test a system that allows treatment of the liver in the presence of breathing motion.

Mapping a signal from an external respiratory bellow to treatment locations within the liver allows the ultrasound transducer to be steered in real time to the target location. Using a moving phantom, three metrics were used to compare static, steered, and unsteered sonications: the area of sonications once a temperature rise of 15°C was achieved, the energy deposition required to reach that temperature, and the average rate of temperature rise during the first 10 s of sonication. Steered HIFU in vivo ablations of the porcine liver were also performed and compared to breath-hold ablations.

For the last phantom metric, all groups were found to be statistically significantly different (P ≤ 0.003). However, in the other two metrics, the static and unsteered sonications were not statistically different (P > 0.9999). Steered in vivo HIFU ablations were not statistically significantly different from ablations during breath-holding.

A system for performing HIFU steering during ablation of the liver with breathing motion is presented and shown to achieve results equivalent to ablation performed with breath-holding. Magn Reson Med 000:000-000, 2012. © 2012 Wiley Periodicals, Inc.

A performance metric is defined based on coil sensitivity information which identifies the (R_Y, R_Z) pair that optimally trades off image quality with scan time reduction on a patient-specific basis. Acceleration Apportionment is evaluated using retrospective analysis of contrast-enhanced MR angiography studies, and prospective studies in which optimally apportioned parameters are compared with standard acceleration parameters.

The retrospective studies show strong variability in optimal acceleration parameters between anatomic regions and between patients. Prospective application of apportionment to foot contrast-enhanced MR angiography with an 8-channel receiver array provides a 20% increase in net acceleration with improved contrast-to-noise ratio. Application to 16-channel contrast-enhanced MR angiography of the feet and calves suggests 10% acceleration increase to R > 13 and no contrast-to-noise ratio loss. The specific implementation allows the optimum (R_Y, R_Z) pair to be determined within one minute.

Optimum 2D SENSE acceleration parameters can be automatically chosen on a per-exam basis to allow improved performance without disrupting the clinical workflow. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The first method simply averages magnitude images reconstructed with sensitivity encoding from each shot, whereas the second and third methods rely on sensitivity encoding to estimate the motion-induced phase error for each shot and subsequently use either a direct phase subtraction or an iterative conjugate gradient algorithm, respectively, to correct for the resulting artifacts. Numerical simulations and in vivo experiments on healthy volunteers were performed to assess the performance of these methods.

The first two methods suffer from a low signal-to-noise ratio or from residual artifacts in the reconstructed diffusion-weighted images and fractional anisotropy maps. In contrast, the third method provides high-quality, high-resolution diffusion tensor imaging results, revealing fine anatomical details such as a radial diffusion anisotropy in cortical gray matter.

The proposed sensitivity encoding + conjugate gradient method can inherently and effectively correct for phase errors, signal loss, and aliasing artifacts caused by both rigid and nonrigid motion in multishot spiral diffusion tensor imaging, without increasing the scan time or reducing the signal-to-noise ratio. Magn Reson Med 000:000–000, 2013. © 2013 Wiley Periodicals, Inc.

A novel two-dimensional (2D) navigator technique was implemented in concert with flow-sensitive alternating inversion recovery (FAIR) preparation and true fast imaging with steady precession (True-FISP) readout. The navigator images were obtained with a low-resolution fast low angle shot readout at end of each arterial spin labeling acquisition. A retrospective algorithm was developed to automatically detect respiratory motion for selective signal averaging. The 2D navigator-gated FAIR True-FISP sequence was performed in ten healthy volunteers and five patients with chronic kidney disease.

Excellent image quality and comparable cortical perfusion rates (healthy: 276 ± 28 mL/100 g/min, patients: 155 ± 25 mL/100 g/min) to literature values were obtained. An average of 3-fold signal-to-noise ratio improvement was obtained in the 2D navigator-gated approach compared with the breath-hold acquisition in healthy volunteers. Good image quality was achieved in patients while the results from breath-hold acquisition were unusable. The quantitative perfusion rates were significantly lower in chronic kidney disease patients compared with the healthy volunteers.

2D navigator-gated free breathing arterial spin labeling is feasible and is a noninvasive method to evaluate renal perfusion both in healthy subjects and those with chronic kidney disease. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The proposed approach for oxygen partial pressure (pO₂) estimation is based on intravoxel incoherent motion diffusion MRI and the dependence of the blood R₂ relaxation rate on the inter-echo spacing measured using a multiple spin-echo Carr-Purcell-Meiboom-Gill sequence and weak-field diffusion model. The accuracy of the approach was validated by comparison with ¹⁹F MRI oximetry.

The results in eight rats at 4.7 T showed that tumors have longer T₁ (1980 ± 186 ms) and T₂ (59 ± 9 ms) relaxation times, heterogeneous blood volume fraction (0.23 ± 0.1), oxygen saturation level (Y) (0.53 ± 0.12), and pO₂ (36 ± 15 mmHg) distributions compared with normal muscle (T₁ 1480 ± 86 ms, T₂ 29 ± 2 ms, blood volume fraction 0.22 ± 0.03, Y 0.49 ± 0.06, and pO₂ 39 ± 5 mmHg). pO₂ estimates based on the novel ¹H approach were essentially identical with ¹⁹F observations.

The study indicates that noninvasive measurement of tumor pO₂ using ¹H MRI derived multiparametric maps is feasible and could become a valuable tool to evaluate tumor hypoxia.

Atherosclerotic plaques from 10 patients (three asymptomatic and seven symptomatic) were investigated. Plaque vulnerability was classified using ultrasound and immunohistochemistry and correlated to Fe(III) measured by electron paramagnetic resonance spectroscopy.

Large intra-plaque Fe(III) variations were found. Plaques from symptomatic patients had a higher Fe(III) concentration as compared with asymptomatic plaques (0.36 ± 0.21 vs. 0.06 ± 0.04 nmol Fe(III)/mg tissue, P < 0.05, in sections adjoining narrowest part of the plaques). All but one plaque from symptomatic patients showed signs of cap rupture. No plaque from asymptomatic patients showed signs of cap rupture. There was a significant increase in cap macrophages in plaques from symptomatic patients compared with asymptomatic patients (31 ± 11% vs. 2.3 ± 2.3%, P < 0.01).

Fe(III) distribution varies substantially within atherosclerotic plaques. Plaques from symptomatic patients had significantly higher concentrations of Fe(III), signs of cap rupture and increased cap macrophage activity. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Spatial resolution, echo, and readout times were varied to determine their influence on the distribution of the blood oxygen level dependent signal. High-resolution co-localized images were used to classify the signal according to its origin in veins or tissue.

High-quality activation maps were obtained with both sequences. Signal contributions from tissue were found to be smaller or slightly larger than from veins. Gradient-echo echo-planar imaging yielded lower ratios of micro-/macro-vascular signals of around 0.6 than spin-echo based functional MRI, where this ratio varied between 0.75 and 1.02, with higher values for larger echo and shorter readout time.

This study demonstrates the feasibility of human functional MRI at 9.4 T with high spatial specificity. Although venous contributions could not be entirely suppressed, venous effects in spin-echo echo-planar imaging are significantly reduced compared with gradient-echo echo-planar imaging. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

An analytical analysis of the OGSE modulation spectrum was provided. Based on this analysis and thorough simulation experiments, the OGSE acquisition was optimized in terms of diffusion waveform shape, waveform timing, and sequence timing—to achieve higher diffusion sensitivity and better sampling of the diffusion spectrum.

The trapezoid-cosine waveform was found to be the optimal OGSE waveform. At the three employed peak encoding frequencies of 18 Hz, 44 Hz, and 63 Hz, the waveform polarity for the least blurry sampling of the diffusion spectrum was 90+/180−, 90+/180+, and 90+/180+, respectively. For the highest diffusion-to-noise ratio at 63 Hz, the b-value was 200 s/mm² and the echo time was 116 ms. Using the optimized sequence, a frequency dependence of the measured apparent diffusion coefficients was observed in white matter-dominant regions such as the corpus callosum.

The obtained results demonstrate, for the first time, the potential of using an OGSE acquisition for investigating microstructure information on a human MR system. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

Despite numerous publications describing the ability of prospective motion correction to improve image quality in magnetic resonance imaging of the brain, a reliable approach to assess this improvement is still missing. A method that accurately reproduces motion artifacts correctable with prospective motion correction is developed, and enables the quantification of the improvements achieved.

A software interface was developed to simulate rigid body motion by changing the scanning coordinate system relative to the object. Thus, tracking data recorded during a patient scan can be used to reproduce the prevented motion artifacts on a volunteer or a phantom. The influence of physiological motion on image quality was investigated by filtering these data. Finally, the method was used to reproduce and quantify the motion artifacts prevented in a patient scan.

The accuracy of the method was tested in phantom experiments and in vivo. The calculated quality factor, as well as a visual inspection of the reproduced artifacts shows a good correspondence to the original.

Precise reproduction of motion artifacts assists qualification of prospective motion correction strategies. The presented method provides an important tool to investigate the effects of rigid body motion on a wide range of sequences, and to quantify the improvement in image quality through prospective motion correction. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Computer-aided design software was used to produce a customized phantom using a rapid prototyping printer. Automated registration algorithms were used on three-dimensional images of the phantom to allow system stability to be easily monitored over time.

The design of the custom phantom allowed reliable placement relative to the imaging coil. Automated registration showed superior ability to detect gradient changes reflected in the images than with manual measurements. Registering images acquired over time allowed monitoring of gradient drifts of less than one percent.

A low cost, MRI compatible phantom was successfully designed using computer-aided design software and a three-dimensional printer. Registering phantom images acquired over time allows monitoring of gradient stability of the MRI system. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

This retrospective study included 17 women (27 fibroids) who underwent uterine arterial embolization for fibroids. MR imaging (1.5 T) was performed before, 1 week and 6 months after uterine arterial embolization. The volume, T2 signal, T1 signal, enhancement after contrast media injection, DWI signal (b = 500 s/mm²) and apparent diffusion coefficient (ADC) were assessed for fibroids.

DWI signal or ADC, whether before or 1 week after the procedure, did not show a statistical relationship to success of uterine arterial embolization. On the 1-week follow-up, 22% of fibroids enhanced vs. 85% on baseline, P < 0.0001 and DW signal intensity increased. ADC values in fibroids decreased between baseline and 1-week (1.61 vs. 1.53 × 10⁻³ mm²/s, P = 0.13). On 6-months, ADC continued to decrease compared with baseline (1.27 × 10⁻³ mm²/s, P = 0.002), but with a lower signal on DWI. No changes were observed in myometrium ADC at any time point.

Our study demonstrated that DWI and ADC reflected early and delayed changes in fibroids after embolization; however, we were not able to demonstrate a statistically significant relationship with outcome. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Gradient-induced eddy currents affect the MRI data acquisition by gradient delays and phase errors that may lead to severe image artifacts for non-Cartesian imaging scenarios such as radial trajectories. While gradient delays are dealt with by respective shifts of the acquisition window during radial image acquisition, this work introduces a simple method for quantifying and correcting phase errors from the actual data prior to image reconstruction. For a given gradient system, the approach yields a specific phase error per gradient that can be used for correcting the raw data.

Phantom studies at 9.4 T demonstrated marked improvements in radial image quality. It could be shown that the phase correction is not compromised by data undersampling. Moreover, the selective correction of gradient-induced phase errors retained the phase information caused by different concentrations of a paramagnetic contrast agent.

The proposed method does not require additional reference measurements and separately corrects for phase errors induced by eddy currents, while retaining the residual phase of the object which may carry physiologic information. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Expressions for the gradient waveform, based on slew and amplitude limits, are developed such that a desired pitch in the spiral k-space trajectory is followed. The source code for this algorithm, written in C, is publicly available. Analytical expressions approximating the spiral trajectory (ignoring the radial component) are given to characterize measurement time, gradient heating, maximum gradient amplitude, and off-resonance phase for slew-limited and gradient amplitude-limited cases. Several numerically calculated trajectories are illustrated, and base Archimedean spirals are compared with analytically obtained results.

Several different waveforms illustrate that the desired slew and amplitude limits are reached, as are the desired undersampling patterns, using the numerical method. For base Archimedean spirals, the results of the numerical and analytical approaches are in good agreement.

A versatile numerical algorithm was developed, and was written in publicly available code. Approximate analytical formulas are given that help characterize spiral trajectories. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

An asymmetric spin-echo echo planar imaging sequence was made frequency-selective to water or a reference substance by controlling the slice-select gradient polarity and the duration of the excitation and refocusing radiofrequency pulses. Images were acquired pairwise, and the temperature-sensitive water images were corrected for field fluctuations using the reference images. In a phantom radiofrequency heating experiment, dissolved dimethyl sulfoxide was used as a reference substance. Temperature stability was tested in vivo on the human brain, referenced using subcutaneous scalp fat. Water and fat phase images were acquired only 50 ms apart. Bloch simulations validated the frequency selection accuracy.

Asymmetric spin-echo imaging using a simple frequency selection method provides highly accurate referenced MR thermometry in phantoms and in vivo at 7 T. Effects of field fluctuations caused by field drift, breathing, and heart beat were corrected. The technique is highly robust against B₁ inhomogeneities.

Frequency selection using gradient-reversal can enable fast accurate referenced in vivo MR thermometry, assisting thermal characterization of radiofrequency coils and possibly in vivo SAR monitoring. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The specific absorption rate (SAR), as the pivotal parameter for quantifying absorbed radiofrequency, increases with the radial dimension of the patient and therefore with the large-scale anatomical properties. The absorbed energy in six human models has been modeled in different Z-positions (head to knees) within a 1.5T bodycoil.

For a fixed incident field, the whole-body SAR can be up to 2.5 times higher (local SAR up to seven times) in obese adult models compared to children. If the exposure is normalized to 4 W/kg whole-body SAR, the local SAR can well-exceed the limits for local transmit coils and shows intersubject variations of up to a factor of three.

The correlations between anatomy and induced local SAR are weak for normalized exposure, but strong for a fixed field, suggesting that anatomical properties could be used for fast SAR predictions. This study demonstrates that a representative virtual human population is indispensable for the investigation of local SAR levels. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

First, an analytical description of magnetization components in the steady state applying WE-UTE was derived and results were compared with numerical simulations based on Bloch's equations. Parameters were optimized for best positive contrast between short-T₂ tissues and fat under consideration of variable relaxation properties over a broad range. Maximal signal yield and signal efficiency of on-resonant protons were compared with UTE sequences with and without off-resonance fat saturation (FatSat). WE-UTE was exemplarily applied for in-vivo musculoskeletal imaging on a 3T whole-body MR unit.

Steady state magnetization of WE-UTE could be described analytically and showed excellent accordance with numerical simulations. Even for tissues with T₂ = 1 ms WE-UTE resulted in 79% of maximal signal yield of UTE without FatSat and was more efficient regarding signal yield if compared with UTE with FatSat. Using WE-UTE in-vivo tendons and ligaments could be well delineated with positive contrast to surrounding fat.

WE-UTE provides a quick method for visualizing short-T₂ tissues with positive contrast. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Segmented 2D-selective radiofrequency excitations can be used to acquire irregularly shaped target regions, e.g., in single-voxel MR spectroscopy, without involving excessive radiofrequency pulse durations. However, segments covering only outer k-space regions nominally use reduced B1 amplitudes (i.e., smaller flip angles) and yield lower signal contributions, which decreases the efficiency of the measurement. The purpose of this study was to show that applying the full flip angle for all segments and scaling down the acquired signal appropriately (signal scaling) retains the desired signal amplitude but reduces the noise level accordingly and, thus, increases the signal-to-noise ratio.

The principles and improvements of signal scaling were demonstrated with MR imaging and spectroscopy experiments at 3 T for a single-line segmentation of a blipped-planar trajectory.

The observed signal-to-noise ration gain depended on the 2D-selective radiofrequency excitation's resolution, field-of-excitation, and its excitation profile and was between 40 and 500% for typical acquisition parameters.

Signal scaling can further improve the performance of measurements with segmented 2D-selective radiofrequency excitations, e.g., for MR spectroscopy of anatomically defined voxels. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

AIFs were measured in aorta/vena cava for five FBV/N mice and in iliac arteries/veins for five NMRI mice with a fast low angle shot sequence, simultaneously with tumor imaging (temporal resolution: 1.19 s). Gadoterate was injected into the tail vein as a bolus (0.286 mmol Gd/kg). An in vitro study was also performed to calculate the relationship between ΔΦ and gadolinium concentration.

The phantom system confirmed the linear relationship between measured ΔΦ and gadolinium concentration. In vivo, a dip in arterial magnitude signal made it impossible to quantify the AIF. With phase imaging, a clear quantifiable bolus peak was obtained; peak measured concentration in plasma was 4.9 ± 0.9 mM for FBV/N mice and 8.0 ± 0.6 mM for NMRI mice, close to the expected concentration of 6.8 mM.

Phase imaging seems to be an appropriate means to measure the AIF of mice at high field. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The cancellation of the crusher and diffusion gradients was demonstrated. Subsequently, crusher gradients were implemented in such a way that they were always orthogonal to the diffusion gradient. Phantom and in-vivo experiments were performed to ascertain that orthogonally implemented crusher gradients alleviate the problem without lowering image quality.

In all experiments, when the crusher gradients' action was cancelled by the diffusion-encoding gradients artifactual signal modulation was observed. When orthogonal gradients were implemented the artifacts were eliminated without detrimental effects on image quality.

Orthogonal crushers are easy to implement and can be used for any variant of diffusion imaging sequences (e.g., DTI, fiber diameter mapping) where the twice-refocused scheme is used. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Coronary MRI still faces major challenges, including lengthy acquisition time, low signal-to-noise-ratio (SNR), and suboptimal spatial resolution. Higher spatial resolution in the sub-millimeter range is desirable, but this results in increased acquisition time and lower SNR, hindering its clinical implementation. In this study, we sought to use an advanced B₁-weighted compressed sensing technique for highly accelerated sub-millimeter whole-heart coronary MRI, and to compare the results to parallel imaging, the current-state-of-the-art, where both techniques were used at acceleration rates beyond what is used clinically. Two whole-heart coronary MRI datasets were acquired in seven healthy adult subjects (30.3 ± 12.1 years; 3 men), using prospective 6-fold acceleration, with random undersampling for the proposed compressed sensing technique and with uniform undersampling for sensitivity encoding reconstruction. Reconstructed images were qualitatively compared in terms of image scores and perceived SNR on a four-point scale (1 = poor, 4 = excellent) by an experienced blinded reader.

The proposed technique resulted in images with clear visualization of all coronary branches. Overall image quality and perceived SNR of the compressed sensing images were significantly higher than those of parallel imaging (P = 0.03 for both), which suffered from noise amplification artifacts due to the reduced SNR.

The proposed compressed sensing-based reconstruction and acquisition technique for sub-millimeter whole-heart coronary MRI provides 6-fold acceleration, where it outperforms parallel imaging with uniform undersampling. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Multibolus TrueFISP-based spin tagging with alternating radiofrequency was developed by taking advantage of the phenomenon that the steady-state signal of TrueFISP is minimally disturbed by periodically inserted magnetization preparations (e.g., spin tagging) that are sandwiched by two α/2 RF pulses. Both theoretical analysis and experimental studies were carried out to optimize the proposed method which was compared with both pulsed and pseudo-continuous arterial spin labeling-based dMRA in healthy volunteers. Optimized multibolus dMRA was also applied in a patient with arteriovenous malformation to demonstrate its potential clinical utility.

Multibolus dMRA offered a prolonged tagging bolus compared to the standard single-bolus dMRA, and allowed improved visualization of the draining veins in the arteriovenous malformation patient. Compared to pseudo-continuous arterial spin labeling-based dMRA, multibolus dMRA provided visualization of the full passage of the labeled blood with the flexibility for both static and dynamic magnetic resonance angiography.

By combining the benefits of pulsed and pseudo-continuous arterial spin labeling-based dMRA, multibolus TrueFISP-based spin tagging with alternating radiofrequency can prolong and enhance the tagging bolus without sacrificing imaging speed or temporal resolution. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The method was tested on phantoms to determine the set of standard 3D spoiled fast gradient echo angles adapted to myocardial T₁ measurements and was compared to the inversion-recovery spin-echo reference T₁ method. Seven volunteers underwent magnetic imaging resonance to acquire myocardial T₁ maps and T₁ values of the human heart.

This original method demonstrated good reproducibility in phantoms and a significant correlation between variable flip angle T₁ values and reference inversion-recovery spin-echo T₁ values. It yielded myocardial T₁ values consistent with expected T₁ and an increasing homogenization of myocardial segments owing to B₁ correction. The mean myocardial T₁ value was 1341 ± 42 ms.

Myocardial 3D T₁ mapping using the variable flip angle approach can potentially be useful for evaluating fibrosis on the entire myocardium using a standard clinical sequence. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

We have shown previously that Minkowski functionals, which are precise morphological and structural descriptors of image heterogeneity, can be used to enhance the detection, in T₁-weighted images, of a targeted Gd³⁺-chelate-based contrast agent for detecting tumor cell death. We have used Minkowski functionals here to characterize heterogeneity in T₂-weighted images acquired before and after drug treatment, and obtained without contrast agent administration.

We show that Minkowski functionals can be used to characterize the changes in image heterogeneity that accompany treatment of tumors with a vascular disrupting agent, combretastatin A4-phosphate, and with a cytotoxic drug, etoposide.

Parameterizing changes in the heterogeneity of T₂-weighted images can be used to detect early responses of tumors to drug treatment, even when there is no change in tumor size. The approach provides a quantitative and therefore objective assessment of treatment response that could be used with other types of MR image and also with other imaging modalities.

Three dynamic imaging applications were chosen: pulmonary perfusion, liver perfusion, and peripheral MR angiography (MRA), with 18, 11, and 10 subjects, respectively. After view-sharing, the k-space data were reconstructed twice: once with channel-by-channel (CBC) followed by sum-of-squares coil combination and once with DVC. Images reconstructed using CBC and DVC were compared and scored based on overall image quality by two experienced radiologists using a five-point scale.

The CBC and DVC showed similar image quality in image domain. Time course measurements also showed good agreement in the temporal domain. CBC and DVC images were scored as equivalent for all pulmonary perfusion cases, all liver perfusion cases, and four of the 10 peripheral MRA cases. For the remaining six peripheral MRA cases, DVC were scored as slightly better (not clinically significant) than the CBC images by Radiologist A and as equivalent by Radiologist B.

For dynamic contrast-enhanced MR applications, it is clinically feasible to reduce image reconstruction time while maintaining image quality and time course measurement using the DVC technique. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The modified CRI algorithm is proposed, which corrects for such biases and yields accurate parametric bound pool fraction f, cross-relaxation rate k, and R₁ maps. Additionally, an analytical correction procedure is introduced to recalculate previously obtained parameter values.

The systematic errors due to unaccounted biexponential relaxation can be characterized as an overestimation of R₁, f, and k, with a relative bias comparable with the magnitude of f. The phantom and human in vivo experiments demonstrate that both proposed modified CRI and analytical correction approaches significantly improve the accuracy of the CRI method.

The accuracy of the CRI method can be considerably improved by taking into account the contribution of magnetization transfer-induced biexponential longitudinal relaxation into variable flip angle R₁ measurements. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

In vivo cartilage MRI with in situ mechanical loading is demonstrated on a clinical 3T system for the patellofemoral as well as for the tibiofemoral knee joint using a T₁-weighted spoiled three-dimensional gradient-echo sequence. Prospective motion correction is performed with a moiré phase tracking system consisting of an in-bore camera and a single tracking marker attached to the skin.

Rigid-body approximation required for prospective correction with optical motion tracking is fulfilled well enough for the patellofemoral as well as for the tibiofemoral joint when the tracking marker is attached to the knee cap and the shin, respectively. Presaturation proves to be efficient in suppressing pulsation artifacts from the popliteal artery and residual motion artifacts primarily arising from nonrigid motion of the posterior knee compartment.

The proposed technique enables knee cartilage imaging under in situ mechanical loading with submillimeter spatial resolution devoid of significant motion artifacts and thus appropriate for cartilage volumetry. It has the potential to provide new insight into the biomechanics of the knee and might complement the panoply of diagnostic MR methods for osteoarthritis. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The balanced steady-state free precession sequence is inherently sensitive to contrast agent enhancement of the myocardium. This sensitivity can be used to advantage in first-pass myocardial perfusion imaging by eliminating the need for magnetization preparation.

Bloch equation simulations, phantom experiments, and in vivo 2D imaging studies were run comparing the proposed technique with three other methods: saturation recovery spoiled gradient echo, saturation recovery steady-state free precession, and steady-state spoiled gradient echo without magnetization preparation. Additionally, an acquisition-reconstruction strategy for 3D perfusion imaging is proposed and initial experience with this approach is demonstrated in healthy subjects and one patient.

Phantom experiments verified simulation results showing the sensitivity of the balanced steady-state free precession sequence to contrast agent enhancement in solid tissue is similar to that of magnetization-prepared acquisitions. Images acquired in normal volunteers showed the proposed technique provided superior signal and signal-to-noise ratio compared with all other sequences at baseline as well as postcontrast.

A new approach to first-pass myocardial perfusion is presented that obviates the need for magnetization preparation and provides high signal-to-noise ratio. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

An approach for ex vivo MR volumetry of human brain hemispheres was developed. Five hemispheres from elderly subjects were imaged ex vivo longitudinally. All datasets were segmented. The longitudinal behavior of volumes measured ex vivo was assessed. The relationship between in vivo and ex vivo volumetric measurements was investigated in seven elderly subjects imaged both antemortem and postmortem.

This approach for ex vivo MR volumetry did not contaminate the results of histopathological examination. For a period of 6 months postmortem, within-subject volume variation across time points was substantially smaller than intersubject volume variation. A close linear correspondence was detected between in vivo and ex vivo volumetric measurements.

Regional brain volumes measured with this approach for ex vivo MR volumetry remain relatively unchanged for a period of 6 months postmortem. Furthermore, the linear relationship between in vivo and ex vivo MR volumetric measurements suggests that this approach captures information linked to antemortem macrostructural brain characteristics. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The lower legs of 34 patients were imaged at 1.5 T with both NCE-MRA and CE-MRA. The NCE-MRA method consisted of a cardiac-gated balanced-SSFP sequence with controllable flow-suppression preparation. Flow-suppressed and unsuppressed datasets were subtracted to obtain angiograms. Two experienced radiologists assessed both NCE-MRA and CE-MRA images, first independently and then in consensus to resolve significant disagreements. Signal loss, vessel conspicuity, vascular disease, venous contamination, artifacts, and diagnostic confidence were assessed.

Using the CE-MRA as the “gold standard,” the per-segment sensitivity and specificity for detection of significant disease were 81.7% and 90.9%, respectively. Mean diagnostic confidence (scale 0–4) was 3.4 for NCE-MRA and 3.9 for CE-MRA. Most vessel segments were well visualized but the popliteal arteries often suffered some technique-related signal loss.

The NCE-MRA method was able to visualize most vessel segments with good or excellent confidence, few artifacts, and excellent background suppression, giving moderate agreement with CE-MRA. However, some segments were poorly visualized, probably due to flow profile distortion in these patients. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The feasibility of the method was examined in five healthy volunteers using a 3 T clinical MRI scanner, at rest and during a sustained isometric contraction. The perfusion of skeletal muscle of the calf was measured using an arterial spin labeling method, whereas the oxygen extraction fraction of the muscle was measured using a susceptibility-based MRI technique.

In all volunteers, the perfusion in soleus muscle increased significantly from 6.5 ± 2.0 mL (100 g min)⁻¹ at rest to 47.9 ± 7.7 mL (100 g min)⁻¹ during exercise (P < 0.05). Although the corresponding oxygen extraction fraction did not change significantly, the rate of oxygen consumption increased from 0.43 ± 0.13 to 4.2 ± 1.5 mL (100 g min)⁻¹ (P < 0.05). Similar results were observed in gastrocnemius muscle but with greater oxygen extraction fraction increase than the soleus muscle.

This is the first MR oximetry developed for quantification of regional skeletal muscle oxygenation. A broad range of medical conditions could benefit from these techniques, including cardiology, gerontology, kinesiology, and physical therapy. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Magnetization transfer asymmetry ratio images of composite meshes were obtained in vitro and in vivo from fast-spin echo acquisitions with frequency saturation offsets of ±3.5 ppm with respect to water frequency and no saturation. Three rats were assessed with APT-MRI each week for 1 month after the intraperitoneal implantation of two meshes, one on each side of the incision. One mesh was coated with collagen and the other was not.

In vitro, meshes were delineated with APT-MRI as a thin continuous linear hypersignal located on one side of the mesh. Unlike collagen-free meshes, collagen-coated meshes were easily identified in vivo with APT-MRI during the first 3 weeks postimplantation. The composite meshes magnetization transfer asymmetry ratio (8.7 ± 2.8%) were significantly different from the muscle magnetization transfer asymmetry ratio value (−0.9 ± 1.6%). After a month, the mesh value dropped down to 1.1 ± 3.9%. Muscle and mesh magnetization transfer asymmetry ratio values were not significantly different and mesh conspicuity was no longer possible.

The results suggest that APT-MRI is a promising technique for noninvasive, early postsurgical visualization of composite meshes used in ventral hernia repair. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

GABA levels in the hypothalamus and occipital cortex (control region) were measured in healthy volunteers during euglycemia and hypoglycemia at 7 tesla using short-echo STEAM (TE = 8 ms, TR = 5 s).

Hypothalamic GABA levels were quantified with a mean within-session test–retest coefficient of variance of 9%. Relatively high GABA levels were observed in the hypothalamus compared with other brain regions. Hypothalamic GABA levels were 3.5 ± 0.3 µmol/g during euglycemia (glucose 89 ± 6 mg/dL) vs. 3.0 ± 0.4 µmol/g during hypoglycemia (glucose 61 ± 3 mg/dL) (P = 0.06, N = 7). In the occipital cortex, GABA levels remained constant at 1.4 ± 0.4 vs.1.4 ± 0.3 µmol/g (P = 0.3, N = 5) as glucose fell from 91 ± 4 to 61 ± 4 mg/dL.

GABA concentration can be quantified in the human hypothalamus and shows a trend toward decrease in response to an acute fall in blood glucose. These methods can be used to further investigate role of GABA signaling in the counterregulatory response to hypoglycemia in humans. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Sixteen volunteers were examined at 1.5 T and 11 returned for a repeat study. The data were analyzed using a distributed parameter (DP) 2-region model to arrive at estimates of F_b, E, blood volume, and interstitial volume. For comparison, estimates of F_b were also obtained using a Fermi function model.

DP model fits were successful in 49 of the 54 data sets. Estimates obtained using DP and Fermi models did not differ for either rest F_b or myocardial perfusion reserve though DP estimates of stress F_b were lower than Fermi estimates. The repeatability of the DP parameters F_b, E, and v_d was better than or equal to the repeatability of Fermi-F_b. E at rest and under stress was estimated to be 66% and 57%, respectively.

The results suggest that characteristics of the microvasculature of healthy myocardium can be reliably determined using dynamic contrast-enhanced MRI at rest and under stress and that delivery of Gd-DTPA to the myocardium is not flow-limited. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The proposed method comprises the following steps: (i) wave generation by a nonmagnetic, piezoelectric driver suitable for integration into the patient table, (ii) fast single-shot 3D wave-field acquisition at four drive frequencies between 30 and 60 Hz, and (iii) single-step postprocessing by a novel multifrequency dual parameter inversion of the wave equation. The method is tested in phantoms, healthy volunteers, and patients with portal hypertension and ascites.

Spatial maps of magnitude and phase of the complex shear modulus were acquired within 6–8 min. These maps are not subject to bias from inversion-related artifacts known from classic MRE. The spatially averaged modulus for healthy liver was 1.44 ± 0.23 kPa with ϕ = 0.492 ± 0.064. Both parameters were significantly higher in the spleen (2.29 ± 0.97 kPa, P = 0.015 and 0.749 ± 0.144, P = 6.58·10⁻⁵, respectively).

The proposed method provides abdominal images of viscoelasticity in a short time with spatial resolution comparable to conventional MR images and improved quality without being compromised by ascites. The new setup allows for the integration of abdominal MRE into the clinical workflow. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

To quantize the effective thermal stress of the tissues, the thermal dose model cumulative equivalent minutes at 43°C was employed, allowing the prediction of thermal tissue damage risk and the identification of potentially hazardous MR scan-scenarios. The numerical results were validated by B₁⁺− and skin temperature measurements.

At continuous 4 W/kg whole-body exposure, peak tissue temperatures of up to 42.8°C were computed for the thermoregulated model (60°C in nonregulated case). When applying cumulative equivalent minutes at 43°C damage thresholds of 15 min (muscle, skin, fat, and bone) and 2 min (other), possible tissue damage cannot be excluded after 25 min for the thermoregulated model (4 min in nonregulated).

The results are found to be consistent with the history of safe use in MR scanning, but not with current safety guidelines. For future safety concepts, we suggest to use thermal dose models instead of temperatures or SAR. Special safety concerns for patients with impaired thermoregulation (e.g., the elderly, diabetics) should be addressed. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A new DREAM echo timing scheme based on the virtual stimulated echo was derived to minimize potential effects of transverse relaxation. Furthermore, the DREAM B₁⁺ mapping performance was investigated in simulations and experimentally in phantoms and volunteers for volumetric applications, studying and optimizing the accuracy of the sequence with respect to saturation effects, slice profile imperfections, and T₁ and T₂ relaxation. Volumetric brain protocols were compiled for different isotropic resolutions (5–2.5 mm) and SENSE factors, and were studied in vivo for different RF drive modes (circular/linear polarization) and the application of dielectric pads.

Volumetric B₁⁺ maps with good SNR at 2.5 mm isotropic resolution were acquired in about 20 s or less. The specific absorption rate was well below the safety limits for all scans. Mild flow artefacts were observed in the large vessels. Moreover, a slight contrast in the ventricle was observed in the B₁⁺ maps, which could be attributed to T₁ and T₂ relaxation effects.

DREAM enables safe, very fast, and robust volumetric B₁⁺ mapping of the brain at ultrahigh fields. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

We obtained MTC images at 9.4 T at three different age points in the Tg2576 mouse model of Alzheimer's disease. The Tg2576 mouse exhibits increased amyloid beta deposition that eventually progresses into amyloid beta plaque formation, increased hyper-phosphorylated tau but does not exhibit neurodegeneration.

Our results show an increase in the MTC signal that predates plaque formation and reported learning and memory deficits in the Tg2576 mouse. This increase in the MTC signal was reversed in a model of antioxidant therapy.

MTC magnetic resonance imaging can be used to detect early macromolecular changes in the Tg2576 mouse model of Alzheimer's disease. The source of the MTC contrast is likely complex and warrants further investigation in additional preclinical models that represent early and late stage Alzheimer's disease pathologies. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

A DQF-MT-UTE pulse sequence was implemented on a 14.1 T AVANCE III Bruker spectrometer equipped with a Bruker micro2.5-imaging gradient system to obtain images of porcine annulus fibrosus.

The DQF-MT-UTE MRI of the annulus fibrosus of porcine intervertebral disc, where the creation time of the double quantum coherence filtering (DQF) was on a time scale appropriate for excitation of macromolecules, showed stronger signal from the outer layers of the disc than from the inner layers closer to the nucleus pulposus. Similarly, spectroscopic studies showed the same trend in the efficiency of the magnetization transfer (MT) from collagen to water.

DQF-MT filtered UTE MRI of the annulus fibrosus provides new contrast parameters that depend on the concentration of the collagen and on the rate and efficiency of MT of its protons to water. The latter parameters appear to be different for collagen types I and II in the annulus fibrosus. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The experiments were conducted on intact lung biopsy samples of pig, rat, mouse, and human using a Bruker Advance III 500 spectrometer. Thirty-five to 39 metabolites were identified and 23 metabolites were quantified. Principal component analysis, partial least-squares discriminant analysis, and analysis of variance tests were performed in order to compare the metabolic profiles of each animal lung biopsies to those of the human lung.

The metabolic composition between human and pig lung was similar. However, human lung was distinguishable from mouse and rat regarding: Trimethylamine N-oxide and betaïne which were present in rodents but not in human lung, carnitine, and glycerophosphocholine which were present in mouse but not in human lung. Conversely, succinic acid was undetected in rat lung. Furthermore, fatty acids concentration was significantly higher in rodent lungs compared to human lung.

Using the metabolomics by NMR high-resolution magic angle spinning spectroscopy on lung biopsy, samples allowed to highlight that pig lung seems to be close to human lung as regarding its metabolite composition with more similarities than dissimilarities. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

With the knowledge of the field distribution generated by each single coil of the array, both the phases and the amplitudes of each coil current are optimized to maximize the magnitude of the field in a specific location of the body per unit of power transmitted through the array and, consequently, minimizing the whole body specific absorption rate for a given pulse sequence.

Simulations considering the human body show that the proposed method can reduce the whole-body specific absorption rate for a given magnitude at the location of interest by a factor of about 6.3 compared to the classic birdcage current configuration, and by a factor of 3.2 compared to phase-only shimming in a case with significant coupling between the elements of the array.

The proposed method can rapidly provide valuable information pertinent to the optimization of field distributions from transmit arrays. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

To address these challenges, we investigated a new modeling technique using metabolic activity decomposition-stimulated echo acquisition mode. The metabolic activity decomposition-stimulated echo acquisition mode technique separates exchanging from nonexchanging metabolites providing twice the information as conventional techniques.

This allowed for accurate measurements of rates of conversion and of multiple T₁ values simultaneously using a single acquisition.

The additional measurement of T₁ values for the reaction metabolites provides further biological information about the cellular environment of the metabolites. The new technique was investigated through simulations and in vivo studies of transgenic mouse models of cancer demonstrating improved assessments of kinetic rate constants and new T₁ relaxation value measurements for hyperpolarized ¹³C-pyruvate, ¹³C-lactate, and ¹³C-alanine. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Noise from coil preamplifiers and carrier bleed-through are identified as sources of interference. Two different SSB systems were designed for 1.5 T with different noise filtering properties. We show how the differences between the filtered noise profiles impact the received MR signal's dynamic range and image signal-to-noise ratio through simulation, bench measurements, and phantom imaging experiments.

When operating individually in the MR scanner, both SSB systems were shown to minimally impact the original DR_sig and signal-to-noise ratio. Conversely, when all eight channels were operating simultaneously, an average signal-to-noise ratio loss was observed to be 12% in the one system, while a second system with more complex filtering was able to achieve a 3% loss in signal-to-noise ratio.

Successful wireless transmission of multiple SSB-encoded MRI signals is possible as long as channel interference is properly managed through design and simulation. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The bipolar read-out technique induces phase and amplitude errors caused by gradient delays, eddy currents, and frequency-dependent coil sensitivity. In this study, these errors were corrected for jointly with the fat/water separation by modeling the impact of these effects on the signal. This approach did not require acquisition of reference data or modification of the pulse sequence.

Simulations and a phantom experiment were used to investigate the accuracy and noise performance of the technique and compare them with those of a well-established technique using unipolar read-out gradients. Also, the in vivo feasibility was demonstrated for abdominal applications.

The phantom experiment demonstrated similar accuracy of the bipolar and unipolar fat quantification techniques. In addition, the noise performance was shown not to be affected by the added estimations of the phase and amplitude errors for most inter-echo times.

The bipolar technique was found to provide accurate fat quantification with noise performance similar to the unipolar technique given an appropriate choice of inter-echo time. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Phantom studies were performed to determine contributions from other Cr kinase metabolites to the CEST effect from Cr (CrCEST). CEST, T₂, magnetization transfer ratio and ³¹P magnetic resonance spectroscopy acquisitions of the lower leg were performed before and after plantar flexion exercise on a 7T whole-body magnetic resonance scanner on healthy volunteers.

Phantom studies demonstrated that while Cr exhibited significant CEST effect there were no appreciable contributions from other metabolites. In healthy human subjects, following mild plantar flexion exercise, increases in the CEST effect from Cr were observed, which recovered exponentially back to baseline. This technique exhibited good spatial resolution and was able to differentiate differences in muscle utilization among subjects. The CEST effect from Cr results were compared with ³¹P magnetic resonance spectroscopy results showing good agreement in the Cr and phosphocreatine recovery kinetics.

Demonstrated a CEST-based technique to measure free Cr changes in in vivo muscle. The CEST effect from Cr imaging can spatially map changes in Cr concentration in muscle following mild exercise. This may serve as a tool for the diagnosis and treatment of various disorders affecting muscle. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

For this purpose, two groups of rats—healthy and mono-lobar elastase-induced animals—were measured. While being ventilated with a mixture of C₂F₆ and oxygen four diffusion weighted 19F-images where acquired for each animal and corresponding ADC-maps were calculated.

No significant apparent diffusion coefficient (ADC) differences were found between healthy lungs; however, the elastase treated lungs showed a significant increase in ADC.

These results demonstrate that ADC measurements with C₂F₆ are sensitive to the microstructure of rat lungs showing that the diffusion of this gas is limited to different levels in healthy and in emphysematous tissue. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The sequence was based on a golden-angle spiral acquisition. Reconstruction of real-time images allowed creation of an image-based navigator. The expiratory spiral interleaves were then retrospectively cardiac-gated using data binning. TPM data were acquired in 20 healthy volunteers and 10 patients with pulmonary hypertension. Longitudinal and radial myocardial velocities were calculated in the left ventricle and right ventricle.

The image-based navigator was shown to correlate well with simultaneously acquired airflow data in 10 volunteers(r=0.93±0.04). The TPM navigated images had a significantly higher subjective image quality and edge sharpness (P<0.0001) than averaged spiral TPM. No significant differences in myocardial velocities were seen between conventional Cartesian TPM with navigator respiratory-gating and the proposed self-navigated TPM technique, in 10 volunteers. Significant differences in the velocities were seen between the volunteers and patients in the left ventricle at systole and end diastole and in the right ventricle at end diastole.

The feasibility of measuring myocardial motion using a golden-angle spiral TPM sequence was demonstrated, with an image-based respiratory navigator calculated from the TPM data itself. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

To measure the arterial input function (AIF) in a mouse tail at high temporal resolution with signal phase of MR projections.

The technique involves the acquisition of one 2D image before injection, followed by a series of projections before, during, and after contrast injection. Differences in the signal phase, relative to the mean preinjection phase, were calculated and converted into a concentration of Gd.

An AIF with a temporal resolution of 100 ms was measured and verified with colorimetry (in a flow phantom) and mass spectrometry analysis (in vivo). The projection-based AIF is expected to better represent the rapid contrast kinetics in the blood following injection, thus improving the accuracy of quantitative dynamic contrast-enhanced-MRI analysis. Colorimetry experiments confirmed that signal phase is preferred over magnitude for a precise determination of an AIF. In-vivo experiments demonstrate the feasibility of our approach in mice.

AIFs can be measured quickly and precisely using phase from projections. Phase data are sensitive to the flow velocity; but this sensitivity is significantly reduced when flow compensation was used. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Several parallel transmit MRI techniques require knowledge of the transmit radiofrequency field profiles (B). During the past years, various methods have been developed to acquire this information. Often, these methods suffer from long measurement times and produce maps exhibiting regions with poor signal-to-noise ratio and artifacts. In this article, a model-based reconstruction procedure is introduced that improves the robustness of B mapping.

The missing information from undersampled B maps and the regions of poor signal to noise ratio are reconstructed through projection into the space of spherical functions that arise naturally from the solution of the Helmholtz equations in the spherical coordinate system.

As a result, B data over a limited range of the field of view/volume is sufficient to reconstruct the B over the full spatial domain in a fast and robust way. The same model is exploited to filter the noise of the measured maps. Results from simulations and in vivo measurements confirm the validity of the proposed method.

A spherical functions model can well approximate the magnetic fields inside the body with few basis terms. Exploiting this compression capability, B maps are reconstructed in regions of unknown or corrupted values. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

3D affine transformations for different respiratory states (bins) were estimated by using 3D-NAV image acquisitions which were acquired during the startup profiles of a steady-state free precession sequence. The calculated 3D affine transformations were applied to the corresponding high-resolution Cartesian image acquisition which had been similarly binned, to correct for respiratory motion between bins.

Quantitative and qualitative comparisons showed no statistical difference between images acquired with the proposed method and the reference method using a diaphragmatic navigator with a narrow gating window.

We demonstrate that 3D-NAV and 3D affine correction can be used to acquire Cartesian whole-heart 3D coronary artery images with 100% scan efficiency with similar image quality as with the state-of-the-art gated and corrected method with approximately 50% scan efficiency. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Image acceleration was achieved using an eight-channel phased array coil. Undersampled image acquisition was simulated in a series of ventilation images and data was reconstructed for various matrix sizes (48–128) using generalized auto-calibrating partially parallel acquisition. Parallel accelerated r imaging was also performed on five mechanically ventilated pigs.

Optimal acceleration factor was fairly invariable (2.0–2.2×) over the range of simulated resolutions. Estimation accuracy progressively improved with higher resolutions (39–51% error reduction). In vivo r values were not significantly different between the two methods: 0.27 ± 0.09, 0.35 ± 0.06, 0.40 ± 0.04 (standard) versus 0.23 ± 0.05, 0.34 ± 0.03, 0.37 ± 0.02 (accelerated); for anterior, medial, and posterior slices, respectively, whereas the corresponding vertical r gradients were significant (P < 0.001): 0.021 ± 0.007 (standard) versus 0.019 ± 0.005 (accelerated) (cm⁻¹).

Quadruple phased array coil simulations resulted in an optimal acceleration factor of ∼2× independent of imaging resolution. Results advocate undersampled image acceleration to improve accuracy of fractional ventilation measurement with hyperpolarized gas MRI. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Subject motion can severely degrade MR images. A retrospective motion correction algorithm, Gradient-based motion correction, which significantly reduces ghosting and blurring artifacts due to subject motion was proposed. The technique uses the raw data of standard imaging sequences; no sequence modifications or additional equipment such as tracking devices are required. Rigid motion is assumed.

The approach iteratively searches for the motion trajectory yielding the sharpest image as measured by the entropy of spatial gradients. The vast space of motion parameters is efficiently explored by gradient-based optimization with a convergence guarantee.

The method has been evaluated on both synthetic and real data in two and three dimentions using standard imaging techniques. MR images are consistently improved over different kinds of motion trajectories. Using a graphics processing unit implementation, computation times are in the order of a few minutes for a full three-dimentional volume.

The presented technique can be an alternative or a complement to prospective motion correction methods and is able to improve images with strong motion artifacts from standard imaging sequences without requiring additional data. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Data were acquired on a 3T clinical system using 3D Golden Angle radial sampling. Two gastrointestinal catheters incorporating four fiducial 19F markers (65 or 50 µL marker volume) were tracked while being pulled through a gel phantom by an operator inside the MR room with velocities of 2–18 mm/s. During continuous acquisition, k-space profiles were transferred in real-time to an external computer for concurrent reconstruction of 3D 19F images and detection and visualization of marker positions. Based on αthe marker positions, automatic adjustments of 1H imaging planes to facilitate targeted anatomical scanning was implemented.

Mean tracking reliabilities were 94.5 and 83.6% (catheters 1 and 2) for temporal resolutions 185–740 ms. Reconstruction times of 196 ms were achieved. Real-time visual feedback allowed the operator to accurately control the catheter movement. Catheter-guidance for 1H imaging was reliable.

The presented real-time 19F MR based framework for the tracking of 19F labeled devices is applicable to combined 19F and 1H MRI guidance of gastrointestinal devices in vivo. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The proposed 3D DESS sequence works with separate acquisition of a first echo with an echo time (TE₁) of 1.2 ms followed by a more heavily T₂-weighted second echo recorded at time TE₂. Subtraction of images from both echoes leads to positive signal from fibrous tissues, whereas in other tissues as musculature and fat the subtraction signal nearly vanishes due to almost similar signal strength in both echoes. Systematic measurements in healthy volunteers with different sets of pulse repetition time (TR), TE₁, readout bandwidth and flip angle were performed to determine optimal sequence parameters.

The presented 3D sequence with Cartesian readout requires relatively short measuring time, provides reasonable signal-to-noise ratio and can be easily implemented in protocols for clinical musculoskeletal MR imaging. Degenerative changes or tears of tendons, ligaments and fibrocartilage are known to cause increased water content and therefore prolongation of transverse relaxation times, which leads to reduced signal intensities in the “subtraction images.”

Positive contrast of fibrous tissue as demonstrated by the proposed sub-DESS approach provides improved conspicuity and allows for three-dimensional reconstruction especially of structures with curved geometry. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

We measured APEX- and APT-weighted magnetization transfer ratio asymmetry (denoted as APEXw and APTw), apparent diffusion coefficient, T₂, and T₁ images and localized proton spectra in rats with permanent middle cerebral artery occlusion at 9.4 T. Phantoms and theoretical studies were also performed.

Within 1-h postocclusion, APEXw and APTw maps showed hyperintensity (3.1% of M₀) and hypointensity (−1.8%), respectively, in regions with decreased apparent diffusion coefficient. Ischemia increased lactate and gamma aminobutyric acid concentrations, but decreased glutamate and taurine concentrations. Over time, the APEXw contrast decreased with glutamate, taurine, and creatine, whereas the APTw contrast and lactate level were similar. Phantom and theoretical studies suggest that the source of APEXw signal is mainly from proteins at normal pH, whereas at decreased pH, gamma aminobutyric acid and glutamate contributions increase, inducing the positive APEXw contrast in ischemic regions. The APTw contrast is sensitive to lactate concentration and pH, but contaminated from contributions of the faster APEX processes.

Positive APEXw contrast is more sensitive to ischemia than negative APTw contrast. They may provide complementary tissue metabolic information. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Electrical properties tomography is a method to map the conductivity and permittivity using MRI; the B₁⁺ amplitude and phase is required as input. The B₁⁺ phase, however, cannot be measured and is therefore deduced from the measurable transceive phase using the transceive phase assumption. Also, earlier studies showed that the B₁⁺ amplitude is not always required for a reliable conductivity reconstruction; this is the so-called “phase-only conductivity reconstruction.”

Electromagnetic simulations and MRI measurements of phantoms and the human head.

Reconstructed conductivity and permittivity maps based on B₁⁺ distributions at 1.5, 3, and 7T were compared to the expected dielectric properties. The noise level of measurements was also determined.

The transceive phase assumption is most accurate for low-field strengths and low permittivity and in symmetric objects. The phase-only conductivity reconstruction is only applicable at 1.5 and 3T for the investigated geometries. The measurement precision was found to benefit from a higher field strength, which is related to increased signal-to-noise ratio (SNR) and increased curvature of the B₁⁺ field. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The purpose of this work is to design an improved Slice-selective Tunable-flip AdiaBatic Low peak-power Excitation (STABLE) pulse with shorter duration and increased off-resonance immunity to make it suitable for use in a greater range of applications and at higher field strengths. An additional aim is to design a variant of this pulse to achieve B₁-insensitive, fat-suppressed excitation.

The adiabatic SLR algorithm was used to generate a more uniform spectral pulse envelope for this improved radiofrequency pulse for adiabatic slice-selective excitation, called STABLE-2. Pulse parameters were adjusted to design a version of STABLE-2 with a spectral null centered on lipids.

In vivo images obtained of the human brain at 3 and 7 T demonstrate that STABLE-2 provides robust, uniform, slice-selective excitation over a range of B₁ values. Phantom and in vivo knee images obtained at 3 T demonstrate the effectiveness of STABLE-2 for fat suppression.

STABLE-2 achieves B₁-insensitive slice-selective excitation while providing greater off-resonance immunity and a shorter pulse duration, when compared to the original STABLE pulse. In particular, the 9.8-ms STABLE-2 pulse provides slice selectivity over 120 Hz whereas the 21-ms STABLE pulse is limited to 80 Hz off-resonance. B₁-Insensitive fat-suppressed excitation may also be achieved by using a variant of this pulse. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

We present a theory and a corresponding method to compute high-resolution field maps over a large dynamic range.

We derive a closed-form expression for the error in the field map value when computed from two echoes. We formulate an optimization problem to choose three echo times which result in a pair of maximally distinct error distributions. We use standard field mapping sequences at the prescribed echo times. We then design a corresponding estimation algorithm which takes advantage of the optimized echo times to disambiguate the field offset value.

We validate our method using high-resolution images of a phantom at 7T. The resulting field maps demonstrate robust mapping over both a large dynamic range, and in low SNR regions. We also present high-resolution offset maps in vivo using both, GRE and multiecho gradient echo sequences. Even though the proposed echo time spacings are larger than the well known phase aliasing cutoff, the resulting field maps exhibit a large dynamic range without the use of phase unwrapping or spatial regularization techniques.

We demonstrate a novel three-echo field map estimation method which overcomes the traditional noise-dynamic range trade-off. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Using a modified spin-echo pulse sequence, the magnetic flux density induced by externally injected currents and the phase map with injected current effects removed were acquired simultaneously. The low-frequency conductivity was reconstructed from the measured magnetic flux density by the projected current density method, while the high-frequency conductivity was reconstructed using the maps. Three different conductivity phantoms were used to demonstrate low- and high-frequency conductivity characteristics.

A conductivity spectrum at two frequencies was successfully acquired with the proposed scheme. Magnetic resonance electrical impedance tomography is advantageous for seeing an anomaly itself wrapped with a thin insulating membrane. In addition, if the membrane is porous, the membrane property can be quantitatively visualized with magnetic resonance electrical impedance tomography. Magnetic resonance electrical properties tomography does not detect such membranes, which enable it to probe things inside an insulating membrane.

Considering these pros and cons and also the fact that the conductivity of biological tissue changes with frequency, a dual-frequency conductivity imaging incorporating both magnetic resonance electrical impedance tomography and magnetic resonance electrical properties tomography in future animal and human experiments is suggested.

In vivo three-dimensional manganese-enhanced MRI at 100-µm isotropic resolution was used to visualize mouse brains between postnatal days 3 and 11, when cerebellum morphology undergoes dramatic changes. Deformation-based morphometry and volumetric analysis of manganese-enhanced MRI images were used to, respectively, detect and quantify morphological phenotypes in Gbx2-CKO mice. Ex vivo micro-MRI was performed after perfusion-fixation with supplemented gadolinium for higher resolution (50-µm) analysis.

In vivo manganese-enhanced MRI and deformation-based morphometry correctly identified known cerebellar defects in Gbx2-CKO mice, and novel phenotypes were discovered in the deep cerebellar nuclei and the vestibulo-cerebellum, both validated using histology. Ex vivo micro-MRI revealed subtle phenotypes in both the vestibulo-cerebellum and the vestibulo-cochlear organ, providing an interesting example of complementary phenotypes in a sensory organ and its associated brain region.

These results show the potential of three-dimensional MRI for detecting and analyzing developmental defects in mouse models of neurodevelopmental diseases. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

It is well established that the method used to combine signals from different coil elements in multichannel MRI can have an impact on the properties of the reconstructed magnitude image. Using a root-sum-of-squares approach results in a magnitude signal that follows an effective noncentral-χ distribution. As a result, the noise floor, the minimum measurable in the absence of any true signal, is elevated. This is particularly relevant for diffusion-weighted MRI, where the signal attenuation is of interest.

In this study, we illustrate problems that such image reconstruction characteristics may cause in the estimation of fibre orientations, both for model-based and model-free approaches, when modern 32-channel coils are used. We further propose an alternative image reconstruction method that is based on sensitivity encoding (SENSE) and preserves the Rician nature of the single-channel, magnitude MR signal. We show that for the same k-space data, root-sum-of-squares can cause excessive overfitting and reduced precision in orientation estimation compared with the SENSE-based approach.

These results highlight the importance of choosing the appropriate image reconstruction method for tractography studies that use multichannel receiver coils for diffusion MRI acquisition. Magn Reson Med, 2013. ©2013 Wiley Periodicals, Inc.

Three-dimensional cine, retrospective respiratory-gated, gradient echo imaging was performed in six adolescents being evaluated for polycystic ovary syndrome, a disorder with a high obstructive sleep apnea prevalence. A novel retrospective gating scheme, synchronized to flow from a nasal cannula, limited image acquisition to predefined physiological ranges. Images were evaluated with respect to contrast, airway signal leakage, and demonstration of dynamic airway area changes.

Two patients were diagnosed with obstructive sleep apnea. Motion artifacts were absent in all image sets. Scan efficiency ranged from 48 to 88%. Soft tissue-to-airway contrast-to-noise ratio varied from 6.1 to 9.6. Airway signal leakage varied between 10 and 17% of soft tissue signal. Automated segmentation allowed calculation of airway area changes over the respiratory cycle. In one severe apnea patient, the technique allowed demonstration of asynchronous airway expansion and contraction above and below a severe constriction.

Retrospective, respiratory gated imaging of the upper airway has been demonstrated, utilizing a gating algorithm to ensure acquisition over specified ranges of respiratory rate and tidal volume. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Poly(lactide-co-glycolide) nanoparticles were engineered to confine superparamagnetic iron oxide contrast for magnetic resonance imaging while enabling controlled drug delivery and targeting to specific cells. To achieve this dual modality, fatty acids were used as anchors for surface ligands and for encapsulated iron oxide in the polymer matrix.

We demonstrate that fatty acid modified iron oxide prolonged retention of the contrast agent in the polymer matrix during degradative release of drug. Antibody-fatty acid surface modification facilitated cellular targeting and subsequent internalization in cells while inducing clustering of encapsulated fatty-acid modified superparamagnetic iron oxide during particle formulation. This induced clustered confinement led to an aggregation within the nanoparticle and, hence, higher transverse relaxivity, r₂, (294 mM⁻¹ s⁻¹) compared with nanoparticles without fatty-acid ligands (160 mM⁻¹ s⁻¹) and higher than commercially available superparamagnetic iron oxide nanoparticles (89 mM⁻¹ s⁻¹).

Clustering of superparamagnetic iron oxide in poly(lactide-co-glycolide) did not affect the controlled release of encapsulated drugs such as methotrexate or clodronate and their subsequent pharmacological activity, thus highlighting the full theranostic capability of our system. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The proposed technique uses one-dimensional self-navigation to track the superior–inferior translation of the heart, with which the acquired three-dimensional radial k-space data is segmented into different respiratory bins. Respiratory motion is then estimated in image space using an affine transform model and subsequently this information is used to perform efficient motion correction in k-space. The performance of the proposed technique on healthy volunteers is compared with the conventional navigator gating approach as well as data binning using diaphragm navigator.

The proposed method is able to reduce the imaging time to 7.1±0.5 min from 13.9±2.6 min with conventional navigator gating. The scan setup time is reduced as well due to the elimination of the navigator. The proposed method yields excellent image quality comparable with either conventional navigator gating or the navigator binning approach.

We have developed a new respiratory motion correction technique for coronary MRA that enables 1 mm³ isotropic resolution and whole-heart coverage with 7 min of scan time. Further tests on patient population are needed to determine its clinical usage. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Principal component analysis allows for accelerated image acquisition with acceptable SNR by filtering noise in projection data, from which pO₂ images are reconstructed. Principal component analysis is used as a denoising technique by including only low-order components to approximate the EPRI projection data.

Simulated and experimental studies show that principal component analysis filtering increases SNR, particularly for small numbers of sub-volumes with changing pO₂, enabling an order of magnitude increase in temporal resolution with minimal deterioration in spatial resolution or image quality.

The SNR necessary for dynamic EPRI studies with temporal resolution required to investigate cycling hypoxia and its physiological implications is enabled by principal component analysis filtering. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

In this pilot study, approved by the institutional review board, 30 patients were investigated comparing whole-heart T₁-weighted dual-echo Dixon CMRA to conventional whole-heart fat-suppressed balanced fast field echo CMRA, integrated into a routine clinical protocol that includes the administration of gadolinium for perfusion and late enhancement measurements. Signal-to-noise-ratio, contrast-to-noise-ratio, and image quality were analyzed.

Dual-echo Dixon significantly (P<0.000001) improved image quality compared with conventional fat-suppressed balanced fast field echo CMRA. Signal-to-noise-ratio and contrast-to-noise-ratio were found to be comparable when balanced fast field echo was performed before gadolinium and dual-echo Dixon fast field echo after gadolinium administration.

Dual-echo Dixon can help to improve whole-heart CMRA image quality significantly. The additional whole-heart fat information delivered by this approach can support a number of new clinical studies addressing the diagnostic and the predictive value of intramyocardial and extramyocardial fatty deposits. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Nine healthy volunteers were recruited, all of whom where scanned at 3 T and 7 T. Three dimensional PCr concentration maps were obtained after images were corrected for B₁ inhomogeneities, T₁ relaxation weighting, and partial volume of fatty tissue in the muscles. Two volunteers performed plantar flexions inside the magnet, and the oxidative capacity of their muscles was estimated.

Three dimensional PCr concentration maps were obtained, with full muscle coverage and nominal voxel size of 0.52 mL at both fields. At 7 T a 2.7-fold increase of signal-to-noise ratio was achieved compared to 3 T.

Imaging ³¹P metabolites at 7 T allowed for significant increase in signal to noise ratio compared to imaging at 3 T, while quantification of the PCr concentration remained unaffected. The importance of such an increase in signal-to-noise ratio is 2-fold, first higher resolution images with reduced partial volume effects can be acquired, and second multiple measurements such as dynamic imaging of PCr post-exercise, ³¹P magnetization transfer, or other ¹H measurements, can be acquired in a single imaging session. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

The extracellular matrix-specific cationized ferritin magnetic resonance imaging probe was injected intravenously into healthy rats and a rat model of the chronic liver disease non-alcoholic steatohepatitis. Rats were subsequently imaged with -weighted magnetic resonance imaging.

This work demonstrates that the binding of cationized ferritin to the perisinusoidal extracellular matrix is reduced by 55% in a rat model of non-alcoholic steatohepatitis compared to healthy controls. This reduced binding is detectable in vivo with magnetic resonance imaging. Immunofluorescence and electron microscopy indicated that the reduced binding is due to inhibited macromolecular access to the perisinusoidal space caused by non-alcoholic steatohepatitis-related microstructural changes.

The reduced accumulation of intravenously injected cationized ferritin may report on changes in macromolecular access to the liver parenchyma in chronic liver disease. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Three different CS-reconstructed 1-shot variable density spirals were explored (corresponding to 28%, 35%, and 46% under-sampling), and compared with conventional 1-shot and 2-shot Archimedean spirals acquired using matched echo time and volume repetition time. fMRI maps were reconstructed with or without CS MRI and sensitivity was compared using identically matched voxels.

The results demonstrated that an l₁-norm based CS reconstruction only led to an increase in functional contrast when applied to 28% under-sampled data. A whole brain t-contrast map revealed that 2-shot uniformly sampled spiral and 28% under-sampled spiral data reconstructed with CS yield equivalent sensitivity, even with matched echo time and volume repetition time

VD spiral exhibits a useful operating range, in the region of 25–30% under-sampling, for which CS reconstruction can be used to increase the sensitivity of fMRI to brain activity. Using CS, VD acquisitions achieve the same sensitivity as 2-shot Archimedean acquisitions, but require only a single shot. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Eddy current-induced phase offsets were measured for different phase-encoding schemes using a higher order dynamic field camera. Based on these measurements, offset phases were corrected for in postprocessing and by run-time phase compensation applying radiofrequency phase increments and additional compensatory gradient areas. The findings were validated using numerical simulations, phantom experiments, and in vivo cardiac scans.

Depending on the phase-encoding scheme, significant eddy current-induced phase offsets were detected. Time-varying phase offsets were observed at subsequent excitations leading to steady-state distortions and hence to profile-dependent amplitude modulations in k-space. Taking into account measured k-space trajectories algebraic image reconstruction allowed compensating imperfect spatial encoding. Correction of amplitude modulations was successfully accomplished by run-time phase compensation.

Using magnetic field monitoring, artifacts in cine balanced steady-state free precession caused by uncompensated eddy current fields can be significantly reduced. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

To develop an improved and generalized technique for correcting T1-related signal fluctuations (T1 effect) in cardiac-gated functional magnetie resonance imaging (fMRI) data with flip angle estimation.

Spatial maps of flip angle and T1 are jointly estimated from cardiac-gated time series using a Kalman filter. These maps are subsequently used for removing the T1 effect in the presence of B1 inhomogeneity. The new technique was compared with a prior technique that uses T1 only while assuming a homogeneous flip angle of 90°. The robustness of the new technique is demonstrated with simulated and experimental data.

Simulation results revealed that the new method led to increased temporal signal-to-noise ratio across a large range of flip angles, T1s, and stimulus onset asynchrony means compared to the T1 only approach. With the experimental data, the new approach resulted in higher average gray matter temporal signal-to-noise ratio of seven subjects (84 vs. 48). The new approach also led to a higher statistical score of activation in the lateral geniculate nucleus (P < 0.002).

The new technique is able to remove the T1 effect robustly and is a promising tool for improving the ability to map activation in fMRI, especially in subcortical regions. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

This study describes a fast and precise method for determining volume–time curves for the right ventricle and for the right ventricular outflow tract. The method applies contour detection and includes a feature for identifying the right ventricular outflow tract volume. The segregation of the outflow tract is performed by four-dimensional curved smooth boundary surfaces defined by prespecified anatomical landmarks.

The comparison with manual contour tracing demonstrates that the method is accurate and improves the precision of the measurement. Compared to manual contour tracing the bias is <0.1% ± 4.1% (right ventricle) and −2.6% ± 20.0% (right ventricular outflow tract). The standard deviations of inter- and intraobserver variabilities for determining the volume of the right ventricular outflow tract are reduced to less than half the values of manual contour tracing. The time consumption per patient is reduced from 341 ± 80 min (right ventricle) and 56 ± 11 min (right ventricular outflow tract) using manual contour tracing to 46 ± 9 min for a combined analysis of right ventricle and right ventricular outflow tract.

The analysis of volume–time curves for the right ventricle and its outflow tract discloses new evaluation methods in clinical routine and science. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

For short repetition times (TR), the angular frequency of distinct oscillations in the transient phase of steady-state free precession sequences is proven to be approximately proportional to the actual flip angle: . The result is not influenced by off-resonance and it can be shown that deviations are only of second order in the small parameter .

B1-TRAP makes use of this effect through a frequency analysis of the transient phase of a train of steady-state free precession signals.

In terms of reliability and time efficiency, a two-dimensional multislice implementation was found to be optimal. Unlike many steady-state -mapping methods, the accuracy of B1-TRAP was not impaired by imperfect slice profiles.

Simulations, phantom, and in vivo measurements showed that B1-TRAP offers a good compromise with respect to speed, robustness, and accuracy. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

We use Maxwell equations to find the distribution of magnetic field induced by myelin sheath and axon. We account for both anisotropy of neuronal tissue “magnetic micro-architecture” and anisotropy of myelin sheath magnetic susceptibility.

Model describes GRE signal comprising of three compartments—axonal, myelin, and extracellular. Both axonal and myelin water signals have frequency shifts that are affected by the magnetic susceptibility anisotropy of long molecules forming lipid bilayer membranes. These parts of frequency shifts reach extrema for axon oriented perpendicular to the magnetic field and are zeros in a parallel case. Myelin water signal is substantially non-monoexponential.

Both, anisotropy of neuronal tissue “magnetic micro-architecture” and anisotropy of myelin sheath magnetic susceptibility, are important for describing GRE signal phaseand magnitude. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Pulmonary function test and p_AO₂ imaging were performed on 4 nonsmokers (1 M, 3 F, 56 ± 1.7 years) and 4 smokers (3 M, 1 F, 52 ± 7.5 years) during three visits over the course of 2 weeks. Two measurements were performed per visit. Variability of p_AO₂ was assessed using a mixed-effect model, with an intraclass correlation coefficient calculated for each group. The coefficient of variation of p_AO₂ over the 3-day period was also compared with the coefficient of variation of pulmonary function test results.

Short-term regional variability based on intraclass correlation coefficient was 0.71 for nonsmokers, and 0.63 for smokers, with long-term variability significantly lower at 0.59 and 0.47, respectively. While the coefficient of variation of the average p_AO₂ was similar to the repeatability of the diffusing capacity of CO, it was significantly higher than that of Forced Vital Capacity (P = 0.02).

Short-term and long-term p_AO₂ variability differences were used as an indication of true physiological changes in order to measure technical reproducibility. Smokers show higher physiologic variability and less technical reproducibility. The suggested p_AO₂-imaging technique showed a reasonable regional repeatability in nonsmokers as well as the ability to detect differences between the two groups with similar reproducibility and superior discriminatory ability when compared with pulmonary function tests. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Cine MR and electrocardiogram data were acquired in healthy adult volunteers for validation of the MOG method. Comparison of MOG and electrocardiogram reconstructions was performed based on the image quality for each method, and the difference between MOG and electrocardiogram trigger times. Fetal images were also acquired, their quality evaluated by experienced radiologists, and the theoretical error in the MOG trigger times were calculated.

Excellent agreement between electrocardiogram and MOG reconstructions was observed. The experimental errors in adult MOG trigger times for all five volunteers were ±(7,25, 17, 8, and 13) ms. Fetal images captured normal and diseased cardiac dynamics.

MOG for cine imaging of the fetal myocardium was developed and validated in adults. Using MOG, the first gated MR images of the human fetal myocardium were obtained. Small moving structures were visualized during radial contraction, thus capturing normal fetal cardiac wall motion and permitting assessment of cardiac function. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

SPEED uses skipped PE steps to accelerate MRI scan. Previously, the PE skip size was chosen from prime numbers only. This restriction has been relaxed in this study to allow choice of any integers rather than merely prime numbers. Various sampling patterns were studied under all possible combinations of PE skip size and PE shifts. A criterion based on the rank values of ghost phasor matrices was introduced to evaluate SPEED reconstruction.

The reconstruction quality was found to correlate with the rank value of the ghost phasor matrix and the skipped PE size N. A low-rank value indicates a singular matrix that causes failure of the SPEED reconstruction. Composite numbers combined with appropriately chosen PE shifts yielded satisfactory reconstruction results.

With properly chosen PE shifts, it was found that any integers, including both prime numbers and composite numbers, could be used as PE skip size for SPEED. This finding allows much more flexible data acquisition options that may lead to more freedom in practical implementations and applications. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Hyperpolarized ¹²⁹Xe MRI was performed at three different nonzero diffusion sensitizations (b-value = 12, 20, and 30 s/cm²) in the lungs of four subjects with COPD and four healthy volunteers. The image signal intensities were fit as a function of b-value to obtain anisotropic diffusion coefficient maps for all subjects. The image signal intensities were also fit to a morphological model allowing extraction of length scales associated with the terminal airways: external radius (R), internal radius (r), mean airspace chord length (L_m), and depth of alveolar sleeve (h).

Longitudinal (D_L) and transverse (D_T) anisotropic diffusion coefficients were both significantly increased (both P= 0.004) in the COPD subjects (0.102 ± 0.02 cm²/s and 0.072 ± 0.02 cm²/s, respectively) compared with the healthy subjects (0.083 ± 0.011 cm²/s and 0.046 ± 0.017 cm²/s, respectively). Significant morphological differences were observed between the COPD subjects and healthy volunteers, specifically decreases in h (68 ± 36 µm vs. 95 ± 710 µm, respectively, P = 0.019) and increases in L_m (352 ± 57 µm vs. 253 ± 37 µm, respectively, P = 0.002) consistent with values obtained previously using hyperpolarized ³He MRI in similar subjects.

Diffusion-weighted hyperpolarized ¹²⁹Xe MRI is a promising technique for mapping changes in human lung morphology and may be useful for early detection of emphysema associated with COPD. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Multiple Fourier encoded slabs were combined into one full volume, using a generalized autocalibrating partially parallel acquisitions (GRAPPA) accelerated diffusion-weighted 3D multislab echo planar imaging (EPI) sequence with 2D phase navigation and in-plane motion correction.

Reconstructed data with 1.5-mm³ nominal resolution is presented and shown under the influence of motion and with variable slab thicknesses. The SNR efficiency between diffusion-weighted 3D multislab EPI and DW 2D ss-EPI is compared. Finally, a 1.3-mm³ full brain scan with 45 diffusion directions is presented.

Diffusion-weighted 3D multislab EPI has been presented as an alternative sequence for high-resolution and high-SNR full brain coverage diffusion studies. Compared with the gold standard 2D diffusion-weighted single-shot Echo Planar Imaging, the SNR efficiency is significantly higher. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

To develop R2* mapping techniques corrected for confounding factors and optimized for noise performance.

Conventional R2* mapping is affected by two key confounding factors: noise-related bias and the presence of fat in tissue. Noise floor effects introduce bias in magnitude-based reconstructions, particularly at high R2* values. The presence of fat, if uncorrected, introduces severe protocol-dependent bias. In this work, the bias/noise properties of different R2* mapping reconstructions (magnitude- and complex-fitting, fat-uncorrected, and fat-corrected) are characterized using Cramer-Rao Bound analysis, simulations, and in vivo data. A framework for optimizing the choice of echo times is provided. Finally, the robustness of liver R2* mapping in the presence of fat is evaluated in 28 subjects.

Fat-corrected R2* mapping removes fat-related bias without noise penalty over a wide range of R2* values. Complex nonlinear least-squares fitted and fat-corrected R2* reconstructions that account for the spectral complexity of fat provide robust R2* estimates with low bias and optimized noise performance over a wide range of echo times combinations and R2* values.

The use of complex fitting and fat-correction improves the robustness, noise performance, and accuracy of R2* measurements, and are necessary to establish R2* as quantitative imaging biomarker in the liver. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

Seven subjects were imaged on a 1.5 T MRI system. For multislice quiescent-inflow single-shot MRA, the venous saturation radiofrequency pulse, in-plane saturation radiofrequency pulse, and quiescent interval were applied only once before the first slice.

The mean (standard deviation) measurements for the intra-arterial signal-to-noise ratio were as follows: Cartesian 1 slice—29.3 (5.5); radial 1 slice, 92 views—22.3 (3.6); radial 1 slice, 46 views—18.5 (2.0); radial 2 slices, 46 views—18.3 (3.2); and radial 3 slices, 32 views—21.7 (3.9), normalized for pixel size to 15.8. Horizontal striping was present with multislice radial quiescent-inflow single-shot MRA (especially with the three-slice acquisition) due to variable T₁ relaxation between the concurrently acquired slices, but the image quality remained diagnostic. Vascular pathology in patients with peripheral arterial disease was well shown by all techniques.

Very high undersampling factors in excess of 18 have been demonstrated for nonenhanced MRA using a radial quiescent-inflow single-shot technique, enabling the acquisition of two to three slices per cardiac cycle. Scan time for a complete peripheral MRA could be shortened to 2 min or less. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.

The proposed method is aimed at reducing eddy current (EC) induced distortion in diffusion weighted echo planar imaging, without the need to perform further image coregistration between diffusion weighted and T2 images. These ECs typically have significant high order spatial components that cannot be compensated by preemphasis.

High order ECs are first calibrated at the system level in a protocol independent fashion. The resulting amplitudes and time constants of high order ECs can then be used to calculate imaging protocol specific corrections. A combined prospective and retrospective approach is proposed to apply correction during data acquisition and image reconstruction.

Various phantom, brain, body, and whole body diffusion weighted images with and without the proposed method are acquired. Significantly reduced image distortion and misregistration are consistently seen in images with the proposed method compared with images without.

The proposed method is a powerful (e.g., effective at 48 cm field of view and 30 cm slice coverage) and flexible (e.g., compatible with other image enhancements and arbitrary scan plane) technique to correct high order ECs induced distortion and misregistration for various diffusion weighted echo planar imaging applications, without the need for further image post processing, protocol dependent prescan, or sacrifice in signal-to-noise ratio. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.

To develop and evaluate variable-density spiral first-pass perfusion pulse sequences for improved efficiency and off-resonance performance and to demonstrate the utility of an apodizing density compensation function (DCF) to improve signal-to-noise ratio (SNR) and reduce dark-rim artifact caused by cardiac motion and Gibbs Ringing.

Three variable density spiral trajectories were designed, simulated, and evaluated in 18 normal subjects, and in eight patients with cardiac pathology on a 1.5T scanner.

By using a DCF, which intentionally apodizes the k-space data, the sidelobe amplitude of the theoretical point spread function (PSF) is reduced by 68%, with only a 13% increase in the full-width at half-maximum of the main-lobe when compared with the same data corrected with a conventional variable-density DCF, and has an 8% higher resolution than a uniform density spiral with the same number of interleaves and readout duration. Furthermore, this strategy results in a greater than 60% increase in measured SNR when compared with the same variable-density spiral data corrected with a conventional DCF (P < 0.01). Perfusion defects could be clearly visualized with minimal off-resonance and dark-rim artifacts.

Variable-density spiral pulse sequences using an apodized DCF produce high-quality first-pass perfusion images with minimal dark-rim and off-resonance artifacts, high SNR and contrast-to-noise ratio, and good delineation of resting perfusion abnormalities. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

In this study, we sought to investigate the feasibility of turbo fast three-dimensional (3D) black-blood imaging by combining a 3D motion-sensitizing driven equilibrium rapid gradient echo sequence with compressed sensing.

A pseudo-centric phase encoding order was developed for compressed sensing-3D motion-sensitizing driven equilibrium rapid gradient echo to suppress flow signal in undersampled 3D k-space. Nine healthy volunteers were recruited for this study. Signal-to-tissue ratio, contrast-to-tissue ratio (CTR) and CTR efficiency (CTR_eff) between fully sampled and undersampled images were calculated and compared in seven subjects. Moreover, isotropic high resolution images using different compressed sensing acceleration factors were evaluated in two other subjects.

Wall-lumen signal-to-tissue ratio or CTR were comparable between the undersampled and the fully sampled images, while significant improvement of CTR_eff was achieved in the undersampled images. At an isotropic high spatial resolution of 0.7 × 0.7 × 0.7 mm³, all undersampled images exhibited similar level of the flow suppression efficiency and the capability of delineating outer vessel wall boundary and lumen-wall interface, when compared with the fully sampled images.

The proposed turbo fast compressed sensing 3D black-blood imaging technique improves scan efficiency without sacrificing flow suppression efficiency and vessel wall image quality. It could be a valuable tool for rapid 3D vessel wall imaging. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

Pregnancy complications such as preeclampsia and fetal growth restriction are sometimes thought to be caused by placental abnormalities associated with reduced oxygenation. Oxygen-enhanced MRI (R₁ contrast) and BOLD MRI (R₂* contrast) have the potential to noninvasively investigate this oxygen environment at a range of gestational ages.

Scanning was carried out at 1.5 T under maternal air and oxygen breathing in a single placental slice in 14 healthy pregnant subjects of gestational ages 21–37 weeks. We report R₁ changes using a respiratory-triggered inversion recovery-turbo spin-echo sequence, which is sensitive to changes in PO₂, and R₂* changes using a breathhold multiple gradient-recalled echo sequence sensitive to changes in oxygen saturation.

Significant R₁ increases (P < 0.005, paired t-test) and R₂* decreases (P < 0.0001, paired t-test) between air and oxygen breathing were demonstrated. ΔR₁ decreased with gestational age (P < 0.0005, r = −0.835, Pearson correlation test). No significant effect of gestational age on R₂* change was observed.

The results demonstrate the feasibility of non-invasive investigation of placental oxygenation using MRI and the sensitivity of R₁ oxygen-enhanced MRI to gestational age. The techniques have the potential to provide unique noninvasive biomarkers in compromised pregnancies. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

To develop an arrhythmia-insensitive rapid (AIR) cardiac T₁ mapping pulse sequence for quantification of diffuse fibrosis.

An arrhythmia-insensitive cardiac T₁ mapping pulse sequence was developed based on saturation recovery T₁ weighting, which is inherently insensitive to heart rate and rhythm, and two single-shot balanced steady-state free precession image acquisitions with centric k-space ordering, where T₁ calculation is inherently insensitive to T₂ effects. Its performance against conventional cardiac T₁ mapping based on inversion recovery (i.e., MOLLI) is compared. Phantom experiments (T₁ ranging from 535 to 2123 ms) were performed with heart rate and rhythm simulated at 60 and 120 beats per minute (bpm) and arrhythmia using an external triggering device. Ten human subjects and 17 large animals were scanned precontrast and 5, 10, and 15 min after contrast agent administration.

Compared with the reference T₁ mapping, AIR yielded lower normalized root-mean-square error than MOLLI (8% vs. 3%, respectively, at 60 bpm, 28% vs. 3%, respectively, at 120 bpm, and 22% vs. 3%, respectively, at arrhythmia). In vivo studies showed that T₁ measurements made by MOLLI and AIR were strongly correlated (r = 0.99) but in poor agreement (mean difference = 161.8 ms, upper and lower 95% limits of agreements = 347.5 ms and −24.0 ms).

Our AIR pulse sequence may be clinically useful for assessment of diffuse myocardial fibrosis in patients. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

Partial volume (PV) effects are caused by limited spatial resolution and significantly affect cerebral blood flow investigations with arterial spin labeling. Therefore, accurate PV correction (PVC) procedures are required. PVC is commonly based on PV maps obtained from segmented high-resolution T₁-weighted images. Segmentation of these images is error-prone, and it can be difficult to coregister these images accurately with the single-shot ASL images such as those created by echo-planar imaging (EPI). In this paper, an alternative method for PV map generation is proposed.

The Look-Locker EPI (LL-EPI) acquisition is used for analyzing the T₁-recovery curve and for subsequent PV map generation. The new method was evaluated in five healthy volunteers (mean age 30 ± 3.7 years).

By applying a linear regression method for PVC, a 12% decrease in regression error was reached with the new method.

PV maps extraction from LL-EPI is a viable, possibly superior alternative to the standard approach based on segmentation of high-resolution T₁-weighted images. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

Purpose: Quantification of cerebral blood flow can be accomplished by model-free arterial spin labeling using the quantitative STAR labeling of arterial regions (QUASAR) sequence. The required deconvolution is normally based on block-circulant singular value decomposition (cSVD)/oscillation SVD (oSVD), an algorithm associated with nonphysiological residue functions and potential effects of arterial dispersion. The aim of this work was to amend this by implementing nonlinear stochastic regularization (NSR) deconvolution, previously used to retrieve realistic residue functions in dynamic susceptibility contrast MRI.

To characterize the residue function in model-free arterial spin labeling, and possibly to improve absolute cerebral blood flow quantification, NSR was applied to deconvolution of QUASAR data. For comparison, SVD-based deconvolution was also employed. Residue function characteristics and cerebral blood flow values from 10 volunteers were obtained. Simulations were performed to support the in vivo results.

NSR was able to resolve realistic residue functions in contrast to the SVD-based methods. Mean cerebral blood flow estimates in gray matter were 36.6 ± 2.6, 28.6 ± 3.3, 40.9 ± 3.6, and 42.9 ± 3.9 mL/100 g/min for cSVD, oSVD, NSR, and NSR with correction for arterial dispersion, respectively. In simulations, the NSR-based perfusion estimates showed better accuracy than the SVD-based approaches.

Perfusion quantification by model-free arterial spin labeling is evidently dependent on the selected deconvolution method, and NSR is a feasible alternative to SVD-based methods. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

To assess the blood-tissue distribution of hyperpolarized ¹³C-labeled molecules in vivo.

Spin-echo experiments with simultaneous acquisition of the free induction decay (FID) signal following the excitation pulse and the spin-echo signal, were used to monitor hyperpolarized [1-¹³C]lactate, [1-¹³C]pyruvate, and the perfusion marker, [¹³C]HP001, following their intravenous injection into tumor-bearing mice. Apparent T₂ relaxation times and diffusion coefficients were also measured.

An increasing tumor echo/FID ratio was observed for all three molecules, which could be explained by their extravasation into the tumor interstitial space, where T₂ relaxation times were longer and diffusion coefficients smaller. Inhibition of the monocarboxylate transporter, which decreased by 40% the label exchange between pyruvate and lactate, reduced the increase in the echo/FID ratio for pyruvate and lactate, but not for HP001, demonstrating that some of the increase in the echo/FID ratio was due to cell uptake of lactate and pyruvate. The different relaxation and diffusion behavior of the intravascular and extravascular signals affected measurements of the apparent label exchange rate constants.

Simultaneous collection of both FID and echo signals can provide information on cell uptake thus giving further insight into the kinetics of hyperpolarized ¹³C label exchange. Care is needed when comparing exchange rate constants determined in spin-echo-based studies. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

To present and validate a new method that formalizes a direct link between k-space and wavelet domains to apply separate undersampling and reconstruction for high- and low-spatial-frequency k-space data.

High- and low-spatial-frequency regions are defined in k-space based on the separation of wavelet subbands, and the conventional compressed sensing problem is transformed into one of localized k-space estimation. To better exploit wavelet-domain sparsity, compressed sensing can be used for high-spatial-frequency regions, whereas parallel imaging can be used for low-spatial-frequency regions. Fourier undersampling is also customized to better accommodate each reconstruction method: random undersampling for compressed sensing and regular undersampling for parallel imaging.

Examples using the proposed method demonstrate successful reconstruction of both low-spatial-frequency content and fine structures in high-resolution three-dimensional breast imaging with a net acceleration of 11–12.

The proposed method improves the reconstruction accuracy of high-spatial-frequency signal content and avoids incoherent artifacts in low-spatial-frequency regions. This new formulation also reduces the reconstruction time due to the smaller problem size. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

This study aimed to quantitatively investigate two main magnetization transfer effects at low B₁: the nuclear Overhauser enhancement (NOE) and amide proton transfer in the human brain at 7 T.

The magnetization transfer effects in the human brain were characterized using a four-pool proton model, which consisted of bulk water, macromolecules, an amide group of mobile proteins and peptides, and NOE-related protons resonating upfield. The pool sizes, exchange rates, and relaxation times of these proton pools were investigated quantitatively by fitting, and the net signals of amide proton transfer and NOE were simulated based on the fitted parameters.

The results showed that the four-pool model fitted the experimental data quite well, and the NOE effects in human brain at 7 T had a broad spectrum distribution. The NOE effects peaked at a B₁ of ∼ 1–1.4 μT and were significantly stronger in the white matter than in the gray matter, corresponding to a pool-size ratio ∼ 2:1. As the amide proton transfer effect was relatively small compared with the NOE effects, magnetization transfer asymmetry analysis yielded an NOE-dominated contrast in the healthy human brain in this range of B₁.

These findings are important to identify the source of NOE effects and to quantify amide proton transfer effects in human brain at 7 T. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

To develop and evaluate a technique that uses the k-space lines rejected by prospective respiratory navigator (NAV) to improve the signal-to-noise ratio (SNR) without increasing the scan time.

In conventional image reconstruction, the motion-corrupted k-space lines rejected by the NAV are not used. In this study, a set of translational motion parameters for the NAV-rejected lines and a phase-corrected average for the k-space line are estimated jointly using a maximum-likelihood approach and the information from the corresponding accepted k-space lines. Left coronary artery images were acquired in 10 healthy adult subjects, and the proposed approach incorporating the NAV-rejected lines was compared with the conventional dataset with NAV-accepted lines only, as well as a simple average of all k-space lines, in terms of SNR, normalized vessel sharpness and qualitative image scores on a four-point scale (1 = poor, 4 = excellent). Late gadolinium enhancement images of the left atrium were also acquired in 21 patients with atrial fibrillation pre- or post-pulmonary vein isolation. Images reconstructed with the proposed, conventional, and simple averaging methods were compared in terms of SNR, and subjective image quality on a four-point scale.

For coronary MRI, there was a significant improvement in SNR with the proposed technique, but no significant difference in normalized vessel sharpness or qualitative image scores were observed with respect to the conventional method. Simple averaging resulted in an SNR gain, but significant loss in vessel sharpness and image quality. For late gadolinium enhancement, there was a significant increase in SNR, but no significant differences were observed in subjective image quality scores between the proposed and conventional methods. There was an SNR gain, but image quality loss for simple averaging, when compared with the conventional technique. In both coronary MRI and late gadolinium enhancement, the SNR gain of the proposed method was not significantly different than the maximum theoretical SNR gain.

The proposed technique improves SNR using the additional information from NAV-rejected k-space lines, while providing similar image quality to standard reconstruction using motion-free k-space data only, with no increase in scan time. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

The feasibility of imaging musculoskeletal fibrous tissue components, such as menisci, ligaments, and tendons, with a conventional spoiled gradient echo technique is explored in vivo at 3 T and 7 T.

To this end, the echo time (TE₁) of a conventional Fourier-encoded multicontrast three-dimensional SGPR sequence is minimized by using nonselective excitation pulses, highly asymmetric readouts, and a variable TE₁ along the phase and slice encoding direction. In addition, a fully sampled second echo image (with TE₂ >> TE₁) can be used to highlight components with short transverse relaxation times in a difference image with positive contrast.

Fourier-encoded spoiled gradient echo sequences are able to provide sub-millisecond TE₁ of about 800 μs for typical in-plane resolutions of about 0.5 x 0.5 mm². As a result, high-resolution positive contrast images of fibrous tissues can be generated within clinically feasible scan-time of about 2–7 minutes.

After optimization, Fourier-encoded spoiled gradient echo provides a highly robust and flexible imaging technique for high-resolution positive contrast imaging of fibrous tissue that can readily be used in the clinical routine. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.