Distinguishing viscous from elastic properties in Viscoelastic Response (VisR) ultrasound

Viscoelastic Response (VisR) ultrasound is an acoustic radiation force (ARF)-based imaging method for noninvasively interrogating the viscoelastic properties of tissue. ViSR ultrasound uses two successive ARF impulses delivered to a single region of excitation (ROE) and tracks the micrometer-scale induced displacements. We have previously demonstrated that tracked displacements can be fit to the mass-spring-damper model in order to measure the relaxation time constant, τ, given by the ratio of viscosity to elasticity. Because it is a ratio, we cannot determine a change in τ is due to changes in elasticity, viscosity, or both. However, elasticity and viscosity may be evaluated uniquely by VisR if considered relative to the magnitude of the forcing function. It is hypothesized that their separation enhances discrimination of viscoelastic materials in VisR ultrasound. We demonstrate that VisR is able to isolate elasticity and viscosity from τ in FEM simulated data and experimentally in a gelatin phantom with a soft inclusion.