Maxwell AD. et al., 2020: An investigation of elastic waves producing stone fracture in burst wave lithotripsy

Maxwell AD, MacConaghy B, Bailey MR, Sapozhnikov OA.
Department of Urology, University of Washington School of Medicine, 1959 Northeast Pacific Street, Seattle, Washington 98195, USA.
Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, Washington 98105, USA.
Department of Acoustics, Physics Faculty, Lomonosov Moscow State University, Leninskie Gory, Moscow 119992, Russia.

Abstract

Burst wave lithotripsy is a method to noninvasively fragment urinary stones by short pulses of focused ultrasound. In this study, physical mechanisms of stone fracture during burst wave lithotripsy were investigated. Photoelasticity imaging was used to visualize elastic wave propagation in model stones and compare results to numerical calculations. Epoxy and glass stone models were made into rectangular, cylindrical, or irregular geometries and exposed in a degassed water bath to focused ultrasound bursts at different frequencies. A high-speed camera was used to record images of the stone during exposure through a circular polariscope backlit by a monochromatic flash source. Imaging showed the development of periodic stresses in the stone body with a pattern dependent on frequency. These patterns were identified as guided wave modes in cylinders and plates, which formed standing waves upon reflection from the distal surfaces of the stone model, producing specific locations of stress concentration in the models. Measured phase velocities compared favorably to numerically calculated modes dependent on frequency and material. Artificial stones exposed to bursts produced cracks at positions anticipated by this mechanism. These results support guided wave generation and reflection as a mechanism of stone fracture in burst wave lithotripsy.
J Acoust Soc Am. 2020 Mar;147(3):1607. doi: 10.1121/10.0000847. PMID: 32237849.