Longitudinal Assessment of Quantitative Metrics for Skeletal Muscle Health Using 3D Rotational Shear Wave Elasticity...

Ultrasonic 3D rotational shear wave elasticity imaging (3D-RSWEI) has previously been used to quantify the mechanical properties of muscle with good precision in single timepoint studies. However, to date, the longitudinal variability of these measurements has not been evaluated. Herein, we report the longitudinal measurements of muscle stiffness and anisotropy assessed using 3D-RSWEI over a 3 month period.

3D-RSWEI measurements were made in vivo in the healthy vastus lateralis of 10 participants. Over 3 mo, we quantified the shear wave speed (SWS) along and across the fibers, along with fractional anisotropy (FA) at multiple knee flexion angles (≤45^∘,45^∘,60^∘,90^∘ and 110^∘), and growth coefficients parametrizing the dependence of SWS and fractional anisotropy on applied knee flexion (β_SWS,‖,β_SWS,⊥ and β_FA). The coefficient of variation (CoV) of each SWEI-based metric of interest was also quantified over 3 months.

Throughout the duration of the study and across all participants, SWS measurements were consistent to within 10%CoV, with FA measurements consistent to within 13%. Fitting SWS growth versus knee flexion yielded a β_SWS,‖ of 0.010±0.001(deg^-1) and a β_SWS,⊥ of 0.004±0.001(m/s/deg). Fitting FA growth with knee flexion yielded a β_FA of 0.0029±0.0007(deg^-1). Growth parameters had an average CoV of 8.3% for β_SWS,‖,18.7% for β_SWS,⊥ and 14.8% for β_FA across all participants over 3 months.

The low variability of these SWEI-based metrics over 3 months in healthy volunteers provides a reference for designing longitudinal studies to evaluate their sensitivity to histopathologic changes associated with muscle disease progression.