Burst Wave Lithotripsy for the Treatment of Ureteral Calculi

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 DESCRIPTION (provided by applicant): Significance: Urinary tract stones pose a significant healthcare burden, with costs to the US exceeding $10 billion annually. The impact of stone disease on the healthcare system is expected to continue to grow as risk factors such as diabetes and obesity become more prevalent. Ureteral stones in particular pose a management challenge as they are often symptomatic, and spontaneous passage is a strong function of stone size and location. Watchful waiting in combination with expulsion therapy is the first line approach, but can lead to repeat physician and/or emergency department visits, lost productivity, and stress on the patient. For active intervention, extracorporeal shock wave lithotripsy (SWL) often requires repeat or secondary procedures to achieve stone-free status. Ureteroscopy, a minimally invasive procedure, has greater stone free rates than SWL, but higher complication rates. Technology: Burst wave lithotripsy (BWL) is a novel, noninvasive, method of stone fragmentation that has the potential to significantly improve the management of ureteral stones. BWL uses multi-cycle, low-amplitude pulses of ultrasound rather than shock waves to noninvasively induce stone fracture. This approach has the potential to reduce the risk of injury, procedural complications, and additional procedures, as well as result in a significant reduction in procedural time and cost. Furthermore, the low pulse pressure amplitude used may preclude the need for anesthesia, providing an attractive alternative to watchful waiting. Preliminary Data: In-vitro studies have shown the technology is capable of breaking all common types of stones found in humans. Results also show that the fragment size can be controlled by altering the ultrasound frequency to produce small fragments likely to spontaneously pass without further symptoms. Preliminary studies indicate the pressure levels required to break stones are significantly below the pressure levels required to induce renal injury in a porcine animal study. Specific Aims: This is a fast-track proposal that will use Phase I to address the technical question of how BWL parameters should be altered to treat a stone obstructed within a ureter compared to a stone free in a water bath. This will require assembly of a BWL transducer and amplifier (Phase I Aim 1) and in vitro studies to establish the pressure level and dose (time) required to break stones within a ureteral phantom (Phase I Aim 2). Phase II identifies the acoustic windows and critical structures exposed while targeting ureteral stones (Phase II Aim 1) and designs the commercial prototype transducer specific for those windows and operating the acoustic parameters identified in Phase I (Phase II Aim 2). The BWL system will be guided by an ultrasound imaging system with specialized algorithms to enhance targeting and detect cavitation to monitor and control for injury (Phase II Aim 3). The safety and efficacy of the developed system will be tested in a porcine animal model (Phase II Aims 4, 5).