Impacts of the capsule on estimation of shear viscoelasticity of livers

The impact of the collagenous capsule of livers on the estimation of shear wave speeds in liver tissues is studied. Shear wave is induced using the method of Shear Dispersion Ultrasound Vibrometry (SDUV) and Orthogonal Frequency Ultrasound Vibrometry (OFUV). Shear wave speeds from 100 Hz to 800 Hz are measured at 0.4 mm and 4.9 mm below the capsule of swine livers in vitro. The study finds that the shear speeds of superficial tissues are significantly different from deep tissues. The Voigt, Maxwell, and Zener models are applied to fit the speed measurements and solve for shear moduli. The Zener model provides robust estimates of the moduli with the minimum estimation errors in different tissue conditions. While the Voigt model requires higher frequencies for stable and accurate estimates of shear moduli of livers, the Maxwell and Zener model provides stable estimates with a limited frequency range, which is valuable for SDUV in vivo applications.