Ultrasound imaging metrics to characterize cavitation activity during burst wave lithotripsy

Abstract

Burst wave lithotripsy (BWL) is a noninvasive approach for comminuting kidney stones with short bursts of focused ultrasound. An important practical aspect of this approach is the ability to deliver treatments with a handheld therapy probe integrated with an ultrasound imaging probe to facilitate ultrasound guidance and monitoring. Because cavitation can influence both injury and efficacy for stone comminution, we seek to develop cavitation-related imaging metrics that correlate with stone fragmentation and tissue injury. Toward this end, a Verasonics system was programmed to synchronize therapy and imaging pulses and record B-mode and Doppler data using a P4-2 probe. Imaging data were recorded during BWL exposures at 350 kHz both for in vivo injury experiments in a porcine model and invitro breaking experiments for stones in a kidney phantom. For in vivo exposures, cavitation was detected more sensitively with Doppler than B-mode, and the detection of sustained cavitation in the kidney parenchyma appears to precede the onset of hemorrhagic injury. For in vitro exposures using different pulse lengths and pulse repetition frequencies to break stones, the axial position of a bubble cloud proximal to the stone appears to correlate with efficacy. [Work supported by NIH NIDDK, Grants P01 DK043881 and K01 DK104854.]