NMR in Biomedicine

A novel method based on the echo-time (TE) averaged ¹H MRS method is introduced for estimating cerebral metabolite proton spin–spin (T₂) relaxation times. The technique works by TE averaging across two distinct TE subarrays and using relative signal attenuation effects to calculate T₂. The method was initially validated through simulation procedures and compared directly with results obtained using standard T₂ curve fitting. Subsequently, the technique was used to estimate in vivo T₂ relaxation times for choline-containing compounds, N-acetyl aspartate, and total creatine in 10 healthy adult subjects. The resulting in vivo T₂ values agreed well with precedent literature values and showed excellent within-subject reproducibility. Several key advantages of the new approach are identified and discussed.

We demonstrated that exercising mouse muscle could be investigated at high-field using a combination of a strictly non-invasive experimental set-up, allowing transcutaneous electrical stimulation and force measurements, and various MRI modalities. The typical multislice diffusion weighted images (top) and apparent diffusion coefficient (ADC) maps (bottom) obtained before, during and immediately after the stimulation protocol clearly illustrate the feasibility and the reliability of high resolution MRI at high-field. Note that the gated acquisitions recorded during exercise were free of motion artifacts as illustrated by diffusion weighted images (b=10, 100, 400 and 700 s/mm², top blue subset), thereby leading to reliable measurements of ADC values (bottom blue subset).

The present study hypothesizes that disorders of consciousness (DOC) interrupt the balance between the internal and external awareness networks. Resting-state functional MRI showed that DOC strengthened external awareness against weakened internal awareness. In particular, augmented visuo-motor modulation was involved.

The potential of texture analysis applied to dynamic contrast-enhanced MRI (DCE-MRI) for predicting clinical and pathological response to neoadjuvant chemotherapy (NAC) in a cohort of 58 patients with locally advanced breast cancer (LABC) before NAC is started was evaluated in this study. Several texture features showed statistical significance and potential for prediction of response before the start of treatment, suggesting that texture analysis could provide clinicians with additional information to increase the accuracy in predicting individual response before NAC is started.

An integrated DC multi-coil/radiofrequency system for MR investigations of the in vivo rat brain at 11.7 T is presented and the benefits of DYNAMITE (DYNAmic Multi-coIl TEchnique) B₀ shimming are demonstrated. Improved whole-brain echo-planar imaging (EPI) quality is expected to critically benefit a wide range of preclinical MR research, and will be crucial when signal pathways, cortical circuitry or the brain's default network are studied. DYNAMITE shimming has the potential to replace conventional shim systems in small-bore animal scanners.

SElf-gated Non-Contrast-Enhanced FUnctional Lung imaging (SENCEFUL) is a non-contrast-enhanced technique to obtain highly resolved images of lung morphology, ventilation and perfusion. SENCFUL involves the acquisition of the direct current (DC) self-gating signal which was additionally recorded during imaging in free breathing without electrocardiogram (ECG) triggering. The data are retrospectively sorted according to the DC signal, thereby obtaining time-resolved datasets of cardiac and respiratory motion, which allow the calculation of qualitative functional lung maps by applying the Fourier transform, similar to Fourier decomposition.

Crusher and slice gradients create a substantial diffusion weighting in high-resolution diffusion-weighted stimulated echo acquisitions. This disrupts uniform sampling in rotationally invariant experiments that cannot be fully corrected by accounting for all cross terms of the B matrix. We present a method of compensating for the applied gradients that corrects the disrupted experiment design with improved robustness in parameter estimates.

A noise figure and noise parameter measurement system, which consists of a combination spectrum and network analyzer, preamplifier, programmable power supply, noise source, tuning board, and desktop computer, was developed.

The noise figure of MRI preamplifiers was characterized in strong magnetic fields up to 9.4 T. In most amplifiers, the gain was found to be reduced by the magnetic field, while the noise figure increased. These changes are dependent on the electron mobility and design of the amplifier's semiconductor devices.

We present spectral results showing elevated lactate pool labeling rates in a bleomycin-induced inflammatory model using hyperpolarized 1-¹³C pyruvate. Arguments based on histological and ³¹P spectroscopy suggest that this is a result of metabolism by infiltrating neutrophils, and that lactate imaging may be a useful method for localizing and staging inflammation.

This work investigates diffusional kurtosis and white matter modeling metrics in cuprizone-induced corpus callosum demyelination. We have found that DK and WMM metrics provide complementary information enhancing the sensitivity to the morphological heterogeneity of the process seen in the rostral segment of the corpus callosum, and can be used as markers for the degree of chronic demyelination in this model.

This work analyzed the effects of energy metabolite turnover and vascular perfusion on load-induced T₂ changes in skeletal muscles of young and healthy subjects by combining muscle functional (T₂-weighted) MRI (mfMRI), ³¹P- chemical shift imaging (CSI) and diffusion-weighted MRI. In particular, it was demonstrated that mfMRI-related T₂ increases strongly vary inter-individually and are associated with changes in muscle perfusion and intra-cellular metabolic turnovers as well as with the rate of perceived exertion.

In this work, we evaluated the potential of optimized lung MRI techniques as a completely non-invasive approach for non-small-cell lung cancer (NSCLC) MRI in vivo detection and follow-up in a mouse model of lung adenocarcinoma expressing the luciferase gene. MRI was shown to be a powerful imaging tool able to detect, quantify and longitudinally monitor the development of submillimetric NSCLCs. This is the first study which proves the feasibility of a completely non-invasive MRI quantitative detection of NSCLC in freely-breathing mice.

The new two-dimensional chemical shift imaging (2D-CSI) sequence that acquires both a free induction decay (FID) and an echo in one measurement was evaluated in phantoms and volunteers with a spatial resolution of 48 × 48 in a clinically acceptable measurement time of 22 min. Intramyocellular lipids (IMCLs) in the calf were detected and quantified from TE acquisition with the use of the water signal from the FID acquisition as an internal concentration reference. Spectra showed high spectral resolution with well-separated IMCLs and with minimal voxel bleeding and subcutaneous lipid contamination.

The purpose of this study was to compare temporal changes in post-contrast myocardial T₁ and extracellular volume (ECV) in an established canine model with chronic atrial fibrillation. In 17 animals, post-contrast myocardial T₁ decreased significantly from 872 to 698 ms (p < 0.001), which corresponds to a 24.9% relative reduction. In contrast, ECV increased from 21.0 to 22.0% (p = 0.38), which corresponds to only a 4.5% relative increase. To partially investigate this discrepancy, we quantified collagen volume fraction (CVF) in post-mortem heart tissues of six canines sacrificed at different disease duration (0–22 months). CVF quantified by histology increased from 0.9 to 1.9% (p = 0.56), which agrees better with ECV than with post-contrast myocardial T₁.

A rapid arterial spin labeling-fast imaging with steady-state free precession (ASL-FISP) MRI acquisition was developed for 7- and 9.4-T preclinical MRI scanners providing perfusion-weighted images in less than 2 s. In this initial ASL-FISP implementation, a conventional ASL preparation was combined with a rapid, centrically encoded FISP readout. In vivo ASL-FISP results in healthy and ischemic mouse brains, as well as healthy mouse kidneys, exhibit reliable quantification with minimal artifacts in comparison with true FISP and echo-planar imaging techniques.