Thresholds for sustained bubble cloud generation in burst wave lithotripsy

Abstract

Burst wave lithotripsy (BWL) is a new non-invasive approach for disintegrating kidney stones using tone bursts of sub-megahertz ultrasound. An important advantage of BWL compared to shock wave lithotripsy (SWL) is the rate at which acoustic energy can be delivered without causing cavitation that injures functional renal tissue. BWL treatments capable of breaking stones have been safely delivered to pig kidneys in vivo at a 40 Hz burst repetition frequency, representing a rate of energy delivery well in excess of that used in SWL. To facilitate the design of BWL treatments that safely and optimally break stones, this work focuses on understanding how treatment parameters affect the generation of sustained bubble clouds. High-speed photography and ultrasound imaging were used to characterize the presence and persistence of cavitation activity in vitro. Experiments were conducted for BWL treatments at 335 kHz to evaluate the impact of treatment rate, dissolved gas concentration, volumetric confinement (representing kidney collecting space), and presence/absence of a stone. Threshold pressures for generating cavitation clouds were observed to vary with each of these variables. [Funding support by NIH P01-DK043881, R01-DK092197, K01-DK104854, and NSBRI through NASA NCC 9-58.]