Quantification of in vivo muscle elastic anisotropy factor by steered push beams

Abstract

Through the past few years, ultrasound (US) elastography has been widely applied to quantify muscle anisotropy. Generally, it is performed with an acoustic radiation force push beam that generates shear waves followed by US imaging. Recently, Ngo et al. (2021) proposed to use a steering push beam to comprehensively assess the mechanical properties of transverse isotropic skeletal muscle tissue. Here, we integrate the equation of shear vertical wave mode to the steering push beam method which allows to retrieve the mechanical parameters of anisotropic muscle tissue. Ex vivo experiments showed a good agreement between the tensile anisotropy χE found by our method and by the mechanical tensile tests. In vivo experiments were conducted to evaluate the anisotropy ratio measured by steering push beam method during different isometric contraction intensities. We observed a growing trend of this ratio with the contraction intensity in both fusiform (Biceps brachii) and pennate muscles (Medial gastrocnemius) of two healthy volunteers. Despite this trend was different between the two types of muscle architecture across contractions intensities, the overall difference had about the same magnitude for both volunteers.