Effect of pulse duration and repetition rate on burst wave lithotripsy stone fragmentation in vitro

Abstract

Burst wave lithotripsy (BWL) is a noninvasive technology to fragment urinary stones using short pulses of focused ultrasound. The aim of this study was to assess how different combinations of pulse length and pulse repetition frequency (PRF) impact stone fragmentation rate and cavitation activity in an in vitro-model. Human calcium oxalate stones between 4–7mm were exposed in a tissue phantom with a 350-kHz BWL transducer with a beamwidth of 6 mm. Treatments were delivered in a 45–50% degassed water bath. Ultrasound imaging was used to target the stone and monitor cavitation activity around the stone. Stones were exposed to ten different parameter sets at peak negative pressure = 6.2 MPa in 5-min intervals up to 30 min total. After each interval, the remaining mass of fragments >2mm was measured to determine the rate of comminution. Longer pulse duration generally produced improved fragmentation. Increasing the pulse repetition rate with set pulse duration did not always produce faster comminution. The results suggest that more effective fragmentation may be achieved in BWL by long pulse durations and low PRF. [Work funded by NIDDK, Grants P01 DK043881 and K01 DK104854. Maxwell, Cunitz, and Bailey have consulting agreements with and equity in SonoMotion, Inc.]