Estimation of 2D displacement and strain field in high frequency ultrasound based elastography

Abstract

High frequency ultrasound (HFUS) and intravascular ultrasound (IVUS) based elastography can be utilized for tissue elasticity imaging at a microscopic level. Mechanical strain fields inside the tissue are calculated as the spatial derivatives of estimated displacement fields. A technique for the estimation of 2D displacement fields is presented. Axial and lateral displacements in the imaging plane are estimated by tracking speckle in B-mode images and analyzing phase differences between image spectra. Concept and limitations of the proposed approach are discussed. Results are compared with an approach for 1D axial displacement estimation, which is based on the analysis of radio frequency (RF) echo signals. The implemented techniques were applied to asses skin elasticity and to analyze non-uniform rotational distortions (NURD) in IVUS with rotating single element transducers. Results of in vivo measurements are presented. It is shown that B-mode based strain imaging is feasible, provided that applied strains are sufficiently small to prevent decorrelation of echo signals.