Direct estimation of carotid artery wall shear strain parameters using autocorrelation of high frame rate ultrasound images

The analytic nature of pulse-echo ultrasound allows for displacement tracking with fine axial resolution and strain estimations in tissue (elastography). The use of differential operators in strain calculations, however, can result in noise amplification and loss of specificity. In this paper a new method for direct estimation of Carotid artery wall strain parameters is presented. This method directly estimates the normal (e_xx, e_zz) and shear strains (e_xz, e_zx) on the anterior and posterior walls of human common carotid artery. This method utilizes the properties of local autocorrelation and the relationship between autocorrelation and power spectral density of the analytic RF echo signals. It is also shown that normal and shear strains can be estimated as parameters of an affine transformation. The steps of this new algorithm are based on properties of 2D autocorrelation function of the speckle region undergoing deformation. In vivo results from Carotid arteries of healthy human subjects show consistency over heart cycles.