In vivo assessment of renal tissue viscoelasticity during acute and gradual renal ischemia

Elasticity imaging methods have been used to study kidney mechanical properties and have demonstrated that kidney elasticity changes with disease state. Moreover, recent studies have demonstrated that kidney elasticity is affected by renal blood flow. The purpose of this study is to evaluate the feasibility of Shearwave Dispersion Ultrasound Vibrometry (SDUV) for in vivo measurements of viscoelasticity in healthy swine kidney and to demonstrate that kidney viscoelasticity is affected by renal blood flow. A total of five female pigs were used in these acute in vivo experiments. Shear wave speed dispersion was studied by exciting shear waves in the renal cortex with a mechanical actuator and with acoustic radiation force. Kidney viscoelasticity was studied at baseline renal blood flow (RBF) and 25, 50, 75 and 100% of baseline RBF. In this study we show that shear wave speed is affected by RBF. As a consequence, shear elastic moduli is affected by RBF. The data from this study did not show a clear relation between viscosity and renal blood flow. Moreover, the data from this study indicates that other variables such as local blood flow, pressure, and volume as well as method accuracy need to be measured to illustrate the relationship between shear elasticity and viscosity with acute and chronic kidney processes.