Combining burst wave lithotripsy and ultrasonic propulsion for enhanced kidney stone comminution

Abstract

Burst wave lithotripsy (BWL) and ultrasonic propulsion (UP) are two new focused ultrasound technologies for noninvasively treating kidney stones. BWL applies short, focused bursts of ultrasound to fracture stones. UP employs long-duration bursts of ultrasound to reposition stones and has been successfully tested on humans. We hypothesize that application of low-level UP can improve comminution by reorienting the stone and dislodging intervening fragments from the stone surface. Experiments were performed in a degassed water bath with a polyvinyl chloride tissue phantom mimicking a kidney calyx. An artificial calcite stone was placed in the phantom and aligned with the focus of a 330-kHz BWL transducer with a co-axial P4-2 imaging probe used for UP. Fragmentation size was compared between stones treated with a fixed 5-minute BWL exposure using 20-cycle bursts at 40 bursts/sec, with or without interleaved UP. The results showed improved fragmentation with the combined exposure, with 3 UP bursts/minute resulting in 45% of stone debris < 2mm versus 23% without UP (p = 0.011). Stones treated with UP alone did not fragment. These results suggest UP can improve stone fragmentation by BWL. [Work supported by NIH K01 DK104854 and P01 DK043881, and NSBRI through NASA NCC 9-58.]