Browsing by Author "Caban-Rivera, Diego A."
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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 Reverberant magnetic resonance elastographic imaging using a single mechanical driver(Physics in Medicine & Biology, 2023-02-27) Kabir, Irteza Enan; Caban-Rivera, Diego A.; Ormachea, Juvenal; Parker, Kevin J.; Johnson, Curtis L.; Doyley, Marvin M.Reverberant elastography provides fast and robust estimates of shear modulus; however, its reliance on multiple mechanical drivers hampers clinical utility. In this work, we hypothesize that for constrained organs such as the brain, reverberant elastography can produce accurate magnetic resonance elastograms with a single mechanical driver. To corroborate this hypothesis, we performed studies on healthy volunteers (n = 3); and a constrained calibrated brain phantom containing spherical inclusions with diameters ranging from 4–18 mm. In both studies (i.e. phantom and clinical), imaging was performed at frequencies of 50 and 70 Hz. We used the accuracy and contrast-to-noise ratio performance metrics to evaluate reverberant elastograms relative to those computed using the established subzone inversion method. Errors incurred in reverberant elastograms varied from 1.3% to 16.6% when imaging at 50 Hz and 3.1% and 16.8% when imaging at 70 Hz. In contrast, errors incurred in subzone elastograms ranged from 1.9% to 13% at 50 Hz and 3.6% to 14.9% at 70 Hz. The contrast-to-noise ratio of reverberant elastograms ranged from 63.1 to 73 dB compared to 65 to 66.2 dB for subzone elastograms. The average global brain shear modulus estimated from reverberant and subzone elastograms was 2.36 ± 0.07 kPa and 2.38 ± 0.11 kPa, respectively, when imaging at 50 Hz and 2.70 ± 0.20 kPa and 2.89 ± 0.60 kPa respectively, when imaging at 70 Hz. The results of this investigation demonstrate that reverberant elastography can produce accurate, high-quality elastograms of the brain with a single mechanical driver.