Shearwave dispersion ultrasound vibrometry (SDUV) on swine kidney

Shearwave dispersion ultrasound vibrometry (SDUV) is used to quantify both tissue shear elasticity and shear viscosity by evaluating dispersion of shear wave propagation speed over a certain bandwidth (50 to 500 Hz). The motivation for developing elasticity imaging techniques is the desire to diagnose disease processes. However, it is important to study the mechanical properties of healthy tissues; such data can enhance clinical knowledge and improve understanding of the mechanical properties of tissue. The purpose of this study is to evaluate the feasibility of using SDUV for in vitro measurements of renal cortex shear elasticity and shear viscosity in healthy swine kidneys. Eight excised kidneys from female pigs were used in these in vitro experiments and a battery of tests was performed to gain insight into the material properties of the renal cortex. In these 8 kidneys, the overall renal cortex elasticity and viscosity were 1.81 ± 0.17 kPa and 1.48 ± 0.49 Pa·s, respectively. In an analysis of the material properties over time after excision, there was not a statistically significant difference in shear elasticity over a 24-h period, but a statistically significant difference in shear viscosity was found. Homogeneity of the renal cortex was examined and it was found that shear elasticity and shear viscosity were statistically different within a kidney, suggesting global tissue inhomogeneity. Increases of more than 30% in shear elasticity and shear viscosity were observed after immersion in 10% formaldehyde. Finally, it was found that the renal cortex is rather anisotropic. Two values for shear elasticity and shear viscosity were measured depending on shear wave propagation direction. These various tests elucidated different aspects of the material properties and the structure of the ex vivo renal cortex.