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

Abstract

Introduction: A noninvasive tool to reposition kidney stones could have significant impact in the management of stone disease. Our research group has developed a noninvasive transcutaneous ultrasound device. A review and update of the current status of this technology is provided. Discussion of Technology: Stone propulsion is achieved through short bursts of focused, ultrasonic pulses. The initial system consisted of an eight-element annular array transducer, computer, and separate ultrasound imager. In the current generation, imaging and therapy are completed with one ultrasound system and a commercial probe. This generation allows real-time ultrasound imaging, targeting, and propulsion. Safety and effectiveness for the relocation of calyceal stones have been demonstrated in the porcine model. Role in Endourology:This technology may have applications in repositioning stones as an adjunct to lithotripsy, facilitating clearance of residual fragments after lithotripsy, expelling de novo stones, and potentially repositioning obstructing stones. Human trials are in preparation.

Effect of Stone Size and Composition on Ultrasonic Propulsion Ex Vivo

“…The results also broaden the application of ultrasonic propulsion beyond facilitating the passage of small stones to potentially repositioning a large stone from the ureteropelvic junction into the pelvis or a calyx to relieve pain or to reposition a large stone from a calyx to the pelvis before shock wave lithotripsy or ureteroscopy. 4 It was not tested, but there may be sufficient force to dislodge an obstructing stone in the ureter or to detach a stone forming on tissue or Randall plaque. 6 …”

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.…”

“…[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. Experience from animal studies with this technology has shown that effective targeting to push stones requires user skills, including an understanding of the spatial anatomy of the collecting system, visualization of the stone, and alignment of the acoustic force with the desired stone trajectory.…”

High-intensity ultrasonic waves in fluids

“…In medical ultrasound, radiation force is a basis for new imaging modalities (Sarvazyan et al, 1998;Tanter et al, 2009). Another recent promising application is the ability to noninvasively expel stones from the kidney (Sorensen et al, 2013).…”