Group shear wave based viscoelastic parameter estimation in SWEI: analysis of sources of bias

This study assesses the reliance of group shear wave speed calculations on the spatial dependence (source geometry) of an Acoustic Radiation Force Impulse excitation in viscoelastic materials. Furthermore, this work examines the impact of motion filtering on the reliability of a lookup table approach to viscoelastic parameter determination. An analytic solution which includes the effects of source geometry is used to generate shear wave profiles for multiple viscoelastic materials. For the materials chosen, the analytic solution yields differences < 0.5% in group speed measurements for two different source geometries (F/1.5 and F/3.0 were examined) and a < 3.5% difference caused by an error in lateral source position of 0.25 mm (which could be expected in the presence of phase aberration). Human liver data from a cohort of 43 patients were assessed for viscoelastic parameter determination. The estimated (mu(0)) values were in agreement with other reports in liver with small variability, but the (eta) estimates were shown to have large variability and a dependence upon motion filtering.