In this work, human myocardial motion is studied in an electrical and in an MRI-compatible (pneumatic) version of a specialized, commercially available, human cardiac phantom at 1.5 Tesla using Displacement Encoding with Stimulated Echoes (DENSE). Work is extended to a prototype rodent phantom, designed, manufactured, implemented, and imaged on a high field (7 T) scanner using urethane-elastomers under dynamic conditions. Mechanical properties of phantom composition (including commercially available urethane-elastomers of variable elasticity, poly(glycerol) sebacate (PGS), and polyvinyl acetate (PVA)-elastomeric samples were evaluated with dynamic mechanical analysis (DMA) and atomic force microscopy (AFM). Both phantoms were cyclically driven at 90–100 bpm and were molded to match accurately human and rodent anatomy. Constructed waveforms attained human and rodent torsions that ranged between 0–40° and 0–20°, respectively. The human phantom used PVA elastomer-materials, whereas solid, cylindrical urethane-elastomeric, and PGS samples were tested in the rodent phantom. Measured bulk storage moduli of elasticity varied between 0.7 and 1.06 MPa using the DMA, whereas AFM measurements independently confirmed the graded surface stiffness of elastomers and PGS samples. Displacement maps were generated with DENSE at time intervals ending at 25% of the cardiac cycle (due to the reduced DENSE-MRI SNR at subsequent intervals) and yielded basal, middle, and apical longitudinal displacements that ranged between −4–6, −8–8, and −10–8 mm, respectively. Elicited in-plane strain results yielded LV phantom values during the first five cardiac phases that ranged between 0.03–3.7% for E_xx and 0.03–4.8% for E_yy. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part A 42A: 59–71, 2013.

Low-resolution nuclear magnetic resonance (LR-NMR) relaxometry is a powerful tool that can be harnessed for characterizing constituents in complex materials. Conversion of the relaxation signal into a continuous distribution of relaxation components is an ill-posed inverse Laplace transform problem. The most common numerical method implemented today for dealing with this kind of problem is based on L₂-norm regularization. However, sparse representation methods via L₁ regularization and convex optimization are a relatively new approach for effective analysis and processing of digital images and signals. In this article, a numerical optimization method for analyzing LR-NMR data by including non-negativity constraints and L₁ regularization and by applying a convex optimization solver PDCO, a primal-dual interior method for convex objectives, that allows general linear constraints to be treated as linear operators is presented. The integrated approach includes validation of analyses by simulations, testing repeatability of experiments, and validation of the model and its statistical assumptions. The proposed method provides better resolved and more accurate solutions when compared with those suggested by existing tools. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part A 42A: 72–88, 2013.

Spoiled fast low-angle shot (FLASH) magnetic resonance imaging (MRI) provides a simple contrast, largely independent of the spin-spin relaxation time. Three-dimensional FLASH imaging (3D FLASH) has gained importance due to its simplicity and its ability to produce isotropic, high-resolution images. Nevertheless, 2D FLASH imaging can be more suited than 3D FLASH imaging in various specific applications requiring long repetition time, such as imaging of the proton density (PD), as it allows interleaved slice acquisition rather than consecutive slice acquisition. In practice, however, a slice-selective excitation produces a nonuniform excitation profile, which needs to be taken into account to allow reliable quantitative data analysis. In this work, the influence of the nonuniform excitation profile on the detected signal is modeled as a dimensionless multiplicative correction, function of the flip angle, and the ratio of the repetition time to the spin-lattice relaxation time T₁. This model is validated experimentally by measuring the PD and T₁ MR parameters in a phantom experiment on a 3T clinical scanner. A good accuracy in the estimation of T₁ and in the reconstruction of the PD (weighted by the receiver sensitivity profile) is obtained, for example, a relative error of 3% in T₁ within the range [500, 2000] ms and a precision of 1% in PD. It is also shown how the proposed theory can be extended to magnetization-prepared 2D-spoiled FLASH as well as other variations of the 2D-spoiled FLASH sequence. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part A 42A: 89–100, 2013.