Browsing by Author "McGarry, Matthew D. J."
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Item Correlated noise in brain magnetic resonance elastography(Magnetic Resonance in Medicine, 2021-10-22) Hannum, Ariel J.; McIlvain, Grace; Sowinski, Damian; McGarry, Matthew D. J.; Johnson, Curtis L.Purpose: Magnetic resonance elastography (MRE) uses phase-contrast MRI to generate mechanical property maps of the in vivo brain through imaging of tissue deformation from induced mechanical vibration. The mechanical property estimation process in MRE can be susceptible to noise from physiological and mechanical sources encoded in the phase, which is expected to be highly correlated. This correlated noise has yet to be characterized in brain MRE, and its effects on mechanical property estimates computed using inversion algorithms are undetermined. Methods: To characterize the effects of signal noise in MRE, we conducted 3 experiments quantifying (1) physiomechanical sources of signal noise, (2) physiological noise because of cardiac-induced movement, and (3) impact of correlated noise on mechanical property estimates. We use a correlation length metric to estimate the extent that correlated signal persists in MRE images and demonstrate the effect of correlated noise on property estimates through simulations. Results: We found that both physiological noise and vibration noise were greater than image noise and were spatially correlated across all subjects. Added physiological and vibration noise to simulated data resulted in property maps with higher error than equivalent levels of Gaussian noise. Conclusion: Our work provides the foundation to understand contributors to brain MRE data quality and provides recommendations for future work to correct for signal noise in MRE.Item In vivo estimation of anisotropic mechanical properties of the gastrocnemius during functional loading with MR elastography(Physics in Medicine & Biology, 2023-02-06) Smith, Daniel R.; Caban-Rivera, Diego A.; Williams, L. Tyler; Van Houten, Elijah E. W.; Bayly, Phil V.; Paulsen, Keith D.; McGarry, Matthew D. J.; Johnson, Curtis L.Objective. In vivo imaging assessments of skeletal muscle structure and function allow for longitudinal quantification of tissue health. Magnetic resonance elastography (MRE) non-invasively quantifies tissue mechanical properties, allowing for evaluation of skeletal muscle biomechanics in response to loading, creating a better understanding of muscle functional health. Approach. In this study, we analyze the anisotropic mechanical response of calf muscles using MRE with a transversely isotropic, nonlinear inversion algorithm (TI-NLI) to investigate the role of muscle fiber stiffening under load. We estimate anisotropic material parameters including fiber shear stiffness (${\mu }_{1}$), substrate shear stiffness (${\mu }_{2}$), shear anisotropy ($\phi $), and tensile anisotropy ($\zeta $) of the gastrocnemius muscle in response to both passive and active tension. Main results. In passive tension, we found a significant increase in ${\mu }_{1},$ $\phi ,$ and $\zeta $ with increasing muscle length. While in active tension, we observed increasing ${\mu }_{2}$ and decreasing $\phi $ and $\zeta $ during active dorsiflexion and plantarflexion—indicating less anisotropy—with greater effects when the muscles act as agonist. Significance. The study demonstrates the ability of this anisotropic MRE method to capture the multifaceted mechanical response of skeletal muscle to tissue loading from muscle lengthening and contraction.Item Quantitative effects of off-resonance related distortion on brain mechanical property estimation with magnetic resonance elastography(NMR in Biomedicine, 2021-09-20) McIlvain, Grace; McGarry, Matthew D. J.; Johnson, Curtis L.Off-resonance related geometric distortion can impact quantitative MRI techniques, such as magnetic resonance elastography (MRE), and result in errors to these otherwise sensitive metrics of brain health. MRE is a phase contrast technique to determine the mechanical properties of tissue by imaging shear wave displacements and estimating tissue stiffness through inverse solution of Navier's equation. In this study, we systematically examined the quantitative effects of distortion and corresponding correction approaches on MRE measurements through a series of simulations, phantom models, and in vivo brain experiments. We studied two different k-space trajectories, echo-planar imaging and spiral, and we determined that readout time, off-resonance gradient strength, and the combination of readout direction and off-resonance gradient direction, impact the estimated mechanical properties. Images were also processed through traditional distortion correction pipelines, and we found that each of the correction mechanisms works well for reducing stiffness errors, but are limited in cases of very large distortion. The ability of MRE to detect subtle changes to neural tissue health relies on accurate, artifact-free imaging, and thus off-resonance related geometric distortion must be considered when designing sequences and protocols by limiting readout time and applying correction where appropriate.