Power Doppler-based ultrasound detection of cavitation for burst wave lithotripsy

Abstract

Burst wave lithotripsy (BWL) is a noninvasive method to fragment urinary stones with pulsed focused ultrasound. Cavitation activity produced by ultrasound pulses in BWL can cause multiple effects including stone fragmentation, acoustic shielding, and tissue injury. Monitoring cavitation activity and spatial extent is therefore important to evaluating these effects and determining parameters that maximize effectiveness and safety. In vivo experiments in a porcine model were conducted using a Verasonics ultrasound system to detect the onset and spatial extent of cavitation through synchronized power Doppler ultrasound imaging during 350-kHz BWL exposures to stones and kidney tissue. Kidneys (n = 15) were exposed in vivo to transcutaneous BWL at multiple pressure levels, and cavitation in tissue was found to be detected as an increase in the measured Doppler power by an average of 28.6 dB (range 11–51 dB) over the background. Cavitation occurred at average levels between 5.8 and 8.0 MPa peak negative pressure, depending on targeting location, stone presence, and exposure parameters. Cavitation presence further correlated with gross observation of injury. These studies demonstrate suggest filtered power Doppler imaging can sensitively detect presence of sustained cavitation during burst wave lithotripsy exposures. [Work supported by NIDDK K01 DK104854 and P01 DK043881.]