Sub-surface elastography based on the dynamic shear strain analysis

Abstract

Quantitative acoustical imaging methods estimate the characteristics of the tissue elasticity of a region of interest having somewhat inhomogeneity contrasted to the surrounding soft tissues. The aim of this research is to propose a novel near-field imaging method for the shear wave elastography and sub-wavelength imaging. The proposed imaging methodology utilizes the determinant of a covariance matrix which is composed of the orthogonal pair of the shear strain variations. The image reconstruction theory can be summarized as follows. 1) The distributions of the normal displacement of the skin surface is governed by the 2-dimensional wave equation in the Lamb-wave field. 2) When the single propagating wave front exists on the surface of the tissue without any stiffer regions, therefore, the orthogonal pair of the out-of-surface shear strains are linearly dependent each other. Therefore the determinant of a covariance matrix which is composed of the orthogonal pair of the shear strains becomes zero. 3) When a region of interest having somewhat inhomogeneity exists, scattered wave field arises in the Lamb-wave field. Consequently, the determinant becomes larger than zero because of the independency between the orthogonal pair over the region of the scattered and incident wave field.