Estimation of shear wave speed and shear viscosity with a simplified time-domain model for viscoelastic media

Shear wave elasticity imaging is a non-invasive imaging modality that characterizes the mechanical properties of soft tissue, such as the shear wave speed or shear modulus. Present time-domain methods for shear wave parameter estimation divide the propagation distance by the propagation time to obtain an estimate of the shear wave speed. However, soft tissues are viscoelastic, and the shear viscosity frequently produces large errors in the estimated shear wave speed. To address this problem, a simplified time-domain model for shear wave parameter estimation in viscoelastic media is applied to simulated three-dimensional (3D) shear waves in a viscoelastic medium, where these 3D simulations require high performance computing to evaluate an approximate time-domain Green’s function solution of Navier’s equation that employs a Kelvin-Voigt rheological model. Parameters for the time-domain model are determined from an optimization procedure, then the shear wave speed is estimated from estimated time delays that account for the shear viscosity. Estimates of the shear wave speed are shown at the focal depth and in a two-dimensional region for various parameter combinations. The simplified time-domain viscoelastic model consistently yields smaller errors for the shear wave speed than cross-correlations while simultaneously providing estimates of the shear viscosity.