Assessment of the depth-dependence of the mechanical parameters of a layered medium using surface excitation and motion measurements on the surface

In this study the dynamic behavior of a layered viscoelastic medium in response to the impulsive acoustic radiation force applied to its surface was investigated. To verify our theoretical model, experiments were performed using tissue-like gel-based phantoms of varying mechanical properties. A 3.5 MHz single-element focused transducer was used to apply the radiation force at the surface of the phantoms and a phase-sensitive OCT system was used to track the displacements on the phantom surface. The results of this study demonstrate good agreement between theoretical predictions and experimental measurements. It was demonstrated that layers at different depths introduce responses at different frequencies. Therefore, the proposed model in combination with spectral analysis can be used to evaluate depth dependant distribution of the mechanical properties based the measurements on the tissue surface.