Displacement underestimation correction using shear waves in VisR ultrasound

We have previously proposed an imaging technique called Viscoelastic Response (VisR) ultrasound that uses acoustic radiation force (ARF) impulses to assess the viscoelastic properties of tissue. Using two successive ARF impulses in the same region of excitation and monitoring the induced deformation, VisR fits displacements to the mass-spring-damper mechanical model to measure the relaxation time constant, τ. In this method, ARF pulses are generated by the same transducer that is used to track motion and thus, the tracked displacements are susceptible to underestimation. Displacement underestimation introduces error into measurement of τ. It is hypothesized that by utilizing shear waves to generate displacement and monitoring tissue displacement outside the region of excitation we can better estimate axial displacements and generate τ measurements that more closely represent the material. We demonstrate displacement underestimation in, versus outside of, the ROE and the associated impact on VisR-derived τ using FEM simulations and experimentally using optical tracking in a translucent tissue-mimicking phantom.