Detection and mapping of thermal lesions using dual-mode ultrasound phased arrays

It has long been recognized that thermal lesions formed using high-intensity focused ultrasound (HIFU) exhibit nonlinear behavior that can be detected in pulse-echo ultrasound. Second harmonic imaging of freshly formed thermal lesions have consistently shown significant enhancement in their visualization confirming this nonlinear behavior. In this paper, we describe a post-beamforming nonlinear filtering algorithm based on a second-order Volterra filter (SVF) model that separates the linear and quadratic components of the echo signal leading to significant enhancement of lesion visualization. Images from ex vivo tissue samples are shown to demonstrate the level of contrast enhancement achieved with the SVF-based quadratic filter compared with standard echo and 2nd harmonic imaging results.