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Open Access Research

Focused ultrasound to displace renal calculi: threshold for tissue injury

Yak-Nam Wang1*, Julianna C Simon1, Bryan W Cunitz1, Frank L Starr1, Marla Paun1, Denny H Liggitt2, Andrew P Evan3, James A McAteer3, Ziyue Liu3, Barbrina Dunmire1 and Michael R Bailey1

Author Affiliations

1 Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle, WA 98105, USA

2 Department of Comparative Medicine, University of Washington School of Medicine, 1959 NE Pacific Street, P.O. Box 357115, Seattle, WA 98195, USA

3 Department of Anatomy and Cell Biology, Indiana University School of Medicine, 635 Barnhill Dr., MS 5055, Indianapolis, IN 46202, USA

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Journal of Therapeutic Ultrasound 2014, 2:5  doi:10.1186/2050-5736-2-5

Published: 31 March 2014

Abstract

Background

The global prevalence and incidence of renal calculi is reported to be increasing. Of the patients that undergo surgical intervention, nearly half experience symptomatic complications associated with stone fragments that are not passed and require follow-up surgical intervention. In a clinical simulation using a clinical prototype, ultrasonic propulsion was proven effective at repositioning kidney stones in pigs. The use of ultrasound to reposition smaller stones or stone fragments to a location that facilitates spontaneous clearance could therefore improve stone-free rates. The goal of this study was to determine an injury threshold under which stones could be safely repositioned.

Methods

Kidneys of 28 domestic swine were treated with exposures that ranged in duty cycle from 0%–100% and spatial peak pulse average intensities up to 30 kW/cm2 for a total duration of 10 min. The kidneys were processed for morphological analysis and evaluated for injury by experts blinded to the exposure conditions.

Results

At a duty cycle of 3.3%, a spatial peak intensity threshold of 16,620 W/cm2 was needed before a statistically significant portion of the samples showed injury. This is nearly seven times the 2,400-W/cm2 maximum output of the clinical prototype used to move the stones effectively in pigs.

Conclusions

The data obtained from this study show that exposure of kidneys to ultrasonic propulsion for displacing renal calculi is well below the threshold for tissue injury.

Keywords:
Injury threshold; Kidney stones; Ultrasonic propulsion