Skin Elasticity Measurement Using Finite Element Simulation with Shear Wave Elasticity Imaging

Shear-wave elasticity imaging (SWEI) has been utilized as a quantitative and operator-independent tool to evaluate skin stiffness. In addition, supersonic shear imaging generates oblique wave-propagation angles in linear arrays. The shear moduli of tissues are computed based on the assumption that shear waves travel along the lateral (perpendicular to the ultrasound beam) direction. Hence, wave propagation at oblique angles can result in bias when estimating the shear wave speed, thus limiting the accuracy of skin tissue elasticity measurements. This study investigated the effects of wave propagation at oblique angles on tissue shear modulus reconstruction using in-silico finite element (FE) simulations. Accordingly, FE skin and subcutaneous tissue models were designed. Parallel and oblique shear waves were applied to a FE tissue model. The shear modulus in the model was computed using a time-of-flight-based algorithm for each shear wave propagation. The skin exhibited a higher error in the shear modulus than the subcutaneous tissue for oblique shear-wave propagation. For both the normal and systemic sclerosis (SSc) tissues, the percentage errors in the shear modulus of the skin tissue abruptly increased for oblique shear wave propagation. Therefore, to improve the measurement accuracy of SWEI for the skin, the Bessel-apodized push beam, which generates parallel shear wavefront, should be utilized, which would be beneficial for the early diagnosis of the progression of skin fibrosis caused by SSc.