Nonlinear pulse-echo imaging methods for HIFU-induced lesion visualization

Abstract

We have recently investigated the use of two different nonlinear imaging methods for visualization of HIFU-induced lesions. The hypothesis is that bubble activity at the location of the HIFU beam can be observed using diagnostic ultrasound with proper post-beamforming signal processing of the rf data. In particular, pulse inversion (PI) and quadratic imaging techniques have been investigated for this purpose. Results from over 100 ex vivo tissue experiments clearly demonstrate the superiority of the nonlinear imaging techiques over conventional B-scan imaging in terms of accurate mapping of lesion boundaries. We are currently examining imaging data to determine the use of nonlinear imaging methods for quantitative assessment of tissue damage. In this paper, we will describe a new experimental procedure for determining the existence of bubble activity associated with different levels of exposure to HIFU, from underexposure to overexposure conditions. Images from conventional B-scan will be compared and contrasted with quadratic and pulse inversion images for various levels of exposure. These results continue to support the hypothesis that bubble activity is extremely important in both lesion formation and lesion visualization using ultrasonic techniques.