Abstract
Recently, a system that uses focused ultrasound to expel renal stone fragments from the kidney by radiation force was developed by Shah etal. [Urol. Res. 38, 491–495 (2010)]. A worst-case treatment protocol using this system would require a total exposure time of 10 min, with a spatial peak pulse average intensity (I_SPPA) of 3600 W/cm2 in water (16 MPa peak positive pressure) and a 3% duty cycle. As the system operates above the FDA limits for diagnostic ultrasound, our goal is to verify the safety of the system by determining the threshold for renal injury. A 2-MHz annular array generating I_SPPA up to 29 000 W/cm2 in water was placed on the surface of in vivo porcine kidneys and focused in the proximal parenchyma. Exposures of 10 min duration with varying I_SPPAs and duty cycles were repeated at least 6 times. Mechanical tissue damage and cell viability were evaluated histologically using H&E, PAS, and NADH diaphorase stains. The proportion of samples showing injury was plotted versus duty cycle and I_SPPA. The results indicate that the system to expel renal stones operates below the threshold for kidney injury. [Work supported by NIH DK043881, DK086371, DK092197, and NSBRI through NASA NCC 9–58.]
Published Version
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