In vivo estimation of anisotropic mechanical properties of the gastrocnemius during functional loading with MR elastography

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.
This is the Accepted Manuscript version of an article accepted for publication in Physics in Medicine & Biology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at This article will be embargoed until 2/6/2024.
magnetic resonance elastography, skeletal muscle, stiffness, tension, gastrocnemius
Smith, Daniel R, Diego A Caban-Rivera, L Tyler Williams, Elijah E W Van Houten, Phil V Bayly, Keith D Paulsen, Matthew D J McGarry, and Curtis L Johnson. “In Vivo Estimation of Anisotropic Mechanical Properties of the Gastrocnemius during Functional Loading with MR Elastography.” Physics in Medicine & Biology 68, no. 4 (2023): 045004.