Focused Ultrasound to Expel Calculi from the Kidney: Safety and Efficacy of a Clinical Prototype Device

Abstract

Purpose Focused ultrasound has the potential to expel small stones or residual stone fragments from the kidney, or move obstructing stones to a nonobstructing location. We evaluated the efficacy and safety of ultrasonic propulsion in a live porcine model. Materials and Methods Calcium oxalate monohydrate kidney stones and laboratory model stones (2 to 8 mm) were ureteroscopically implanted in the renal pelvicalyceal system of 12 kidneys in a total of 8 domestic swine. Transcutaneous ultrasonic propulsion was performed using an HDI C5-2 imaging transducer (ATL/Philips, Bothell, Washington) and the Verasonics® diagnostic ultrasound platform. Successful stone relocation was defined as stone movement from the calyx to the renal pelvis, ureteropelvic junction or proximal ureter. Efficacy and procedure time was determined. Three blinded experts evaluated histological injury to the kidney in the control, sham treatment and treatment arms. Results All 26 stones were observed to move during treatment and 17 (65%) were relocated successfully to the renal pelvis (3), ureteropelvic junction (2) or ureter (12). Average ± SD successful procedure time was 14 ± 8 minutes and a mean of 23 ± 16 ultrasound bursts, each about 1 second in duration, were required. There was no evidence of gross or histological injury to the renal parenchyma in kidneys exposed to 20 bursts (1 second in duration at 33-second intervals) at the same output (2,400 W/cm2) used to push stones. Conclusions Noninvasive transcutaneous ultrasonic propulsion is a safe, effective and time efficient means to relocate calyceal stones to the renal pelvis, ureteropelvic junction or ureter. This technology holds promise as a useful adjunct to surgical management for renal calculi.

Content and Face Validation of a Curriculum for Ultrasonic Propulsion of Calculi in a Human Renal Model

“…Ultrasonic propulsion was performed with a custom-built clinical prototype, including an ultrasound imaging transducer (ATL/Philips C5-2 probe), Verasonics Ultrasound Engine (Redmond, WA), computer processor, and touchscreen, as previously described. 2,4 The user identifies a stone under B-mode ultrasound. Touching the stone on the monitor triggers delivery of the acoustic push to the targeted location.…”

“…Safety and effectiveness of the technology to reposition stones has been demonstrated in an animal model. [1][2][3] Potential applications of this technology in the management of upper tract stones include facilitating passage of small stones or residual stones after lithotripsy, pre-or intraoperative repositioning of renal stones, and moving an obstructing stone to a nonobstructing position. 4 A potential barrier to the adoption of this technology by urologists may be the skill required to operate a diagnostic ultrasound imager and interpret ultrasound images.…”

Focused Ultrasonic Propulsion of Kidney Stones: Review and Update of Preclinical Technology

“…The pressure and total energy delivered are less than that in current shockwave lithotripsy treatments. 10,11 Operation of the device is designed for a single user. The stone is visualized using conventional real-time B-mode ultrasound.…”

“…2). 10,11 In 12 kidneys, 26 calyceal stones (2-8 mm in size) and metalized beads (2 mm in size, 0.02 g) were endoscopically placed in the lower or interpolar calyx. Overall, 17 stones or beads (65%) were successfully relocated.…”

“…9 Our research group has developed a transcutaneous, noninvasive ultrasound prototype that uses acoustic force from focused ultrasound waves to reposition stones. [10][11][12][13][14][15] A review and update of the current status of this technology are provided.…”