Analysis of excitation frequency in elasticity reconstruction using the FEM inverse-problem

Multi-frequency harmonic elastography is a technique that involves applying vibrations to tissues in order to measure their mechanical properties. High speed plane wave ultrasound imaging is used to image dynamic deformations produced by a voice coil actuator on a gelatin phantom with a hard inclusion mimicking a focal lesion (e.g. breast, liver). Tissue displacements are estimated from the echo data and used in a finite element inverse elasticity problem. Until now, mostly one or very few frequencies were used for tissue excitation which could lead to inconclusive or misleading results. In this paper we analyze a broad bandwidth of 100 Hz with a fine 5 Hz step and study the effect of the frequency excitation on the inversion of the inclusion geometry and stiffness ratio with respect to background. The results show the importance of using numerous frequencies for tissue excitation, as focal lesions could be "invisible" or have a deformed structure at certain frequencies.