Assessment of shear elasticity and viscosity of tissue using acoustic radiation force applied to a spherical acoustic inhomogeneity.

Abstract

An accurate assessment of mechanical properties of tissue is desired in many applications ranging from biomedical research to medical diagnostics and surgery. Currently, several methods to assess shear elasticity of tissue are available while the techniques to measure tissue viscosity are not yet fully developed. However, shear viscosity is an indicative functional parameter of soft tissue. In addition, the local changes of shear viscosity can affect the accuracy of shear elasticity assessment. Therefore, in this study, an acoustic radiation force approach to assess both shear elasticity and viscosity of tissue is developed. Such approach is based on monitoring of the spatio-temporal displacement of an ultrasound inhomogeneity in response to applied impulsive radiation force. In experiments, a 2-mm-diameter solid sphere was embedded into the gel phantoms with varying shear elasticity and viscosity. The sphere was then perturbed using acoustic radiation force produced by a single-element focused ultrasound transducer operating at 3.5 MHz. The displacement of the sphere was monitored using another single-element focused ultrasound transducer with center frequency of 25 MHz. The results indicate that the temporal characteristics of the displacement can be used to assess both shear elasticity and viscosity of tissues simultaneously and independently. [Work supported by NIH.]