In vivo achilles tendon elasticity assessment using supersonic shear imaging: A feasibility study

In this study shear wave dispersion was measured in vivo in four Achilles tendons by applying the Supersonic Shear Imaging technique and the concept of Shear Wave Spectroscopy parallel and perpendicular to the tendon fiber orientation. In tissues shear wave dispersion is related to two main physical causes: the geometry of the investigated medium which can lead to guided waves and/or the viscosity of the medium (if Voigt model is assumed). By modeling the Achilles tendon as a transverse isotropic plate it was possible to estimate the tendon elastic properties described by the five independent elastic constants (C₁₁, C₃₃, C₁₃, C₅₅ and C₆₆) of the Christoffel´s tensor. We show that parallel to fibers the geometrical effect leading to guided wave propagation is prominent, while perpendicularly to fibers viscosity must be also taken into account to fully describe the experimental data. The obtained results agree with those reported in the literature. In this study we have demonstrated that the use of a dispersion model must be taken into account in order to properly estimate the tendon viscoelastic properties.