Reconstruction of shear moduli in nearly incompressible transversally isotropic media with phase and group velocities of Rayleigh waves

Evaluating deformational properties in soft tissues is crucial to manage their dysfunctions and help guide surgeries. Wave-based Optical Coherence Elastography (OCE) is a relatively new modality in the elastography field. Although it can probe only anterior organs, such as cornea or skin, it can potentially serve major benefits over USE and MRI due to its non-contact manner, real-time acquisition and high spatial resolution. Additional benefits come from OCT and provide reach, 3-D, micron-scale resolution structural and functional information. Different experimental techniques in air-coupled acoustic micro-tapping OCE have been recently proposed to better match clinical environments. However, OCE has not yet become quantitative in mechanical moduli reconstruction mainly due to (i) wave guidance and (ii) the complicated anisotropic structure of anterior tissues. Mechanical moduli of most anisotropic organs probed by OCE can be locally characterized by a nearly incompressible transversally isotropic (NITI) model. To reconstruct all three mechanical moduli of a NITI medium, angular dispersion of Rayleigh-wave phase velocity should be computed. However, it is not easily achievable due to a difference in propagation directions of wave phase and energy. This talk describes spatial dispersion effects in anisotropic soft media for Rayleigh waves. We consider the main geometries: point-like and line sources, and analytically and experimentally show how to process measured velocity spatial dispersion for correct reconstruction of elastic moduli.