Innovations in Ultrasound Technology for the Diagnosis and Treatment of Nephrolithiasis

Since the initial use of ultrasound in the management of kidney stone disease nearly sixty years ago, its role in the diagnosis and treatment of kidney stone disease has rapidly evolved, particularly over the past decade. Refinements in ultrasound imaging technology and novel utilization of acoustic radiation forces have broadened the potential clinical utility for both diagnostic and therapeutic purposes in the management of nephrolithiasis. Our review article highlights the significant progress and recent innovation in the area of ultrasound technology for stone disease and underscores areas for further technology development in the arena of ultrasound-based stone management.

Our group at the University of Washington has focused on the use of medical ultrasound in the management of urinary stone disease. We have built upon the work of other groups in improving the accuracy of ultrasound for stone detection by providing evidence for the etiology of the twinkling artifacts, evaluating adjunctive measures of stone size such as the posterior acoustic shadow, and developing stone-specific ultrasound imaging algorithms to optimize the detection and sizing of kidney stones.^1–3 Use of these research imaging algorithms has demonstrated a sensitivity of 84% for stone detection, with 44% of imaged stones demonstrating a 1 mm size concordance with corresponding CT sizes.³

Novel application of acoustic radiation force has also led to emerging medical technologies such as ultrasonic propulsion and tractor beam technology, which are currently under investigation as novel technologies that allow non-invasive, transcutaneous movement of stones. Potential applications of such technology include re-positioning obstructing stones in the acute setting from the ureteropelvic junction or ureterovesical junction to relieve symptoms, facilitating the clearance of post-lithotripsy stone fragments, and intra-operative re-positioning of stones to more favorable calyces for treatment.^4,5 Results of a second clinical study are currently pending publication and current clinical trials are underway at the University of Washington to better evaluate the clinical utility of ultrasonic propulsion in these settings (NCT02028559, Safety, and Effectiveness of the Ultrasonic Propulsion of Kidney Stones).

New technologies in non-invasive transcutaneous stone fragmentation are also under development at our institution. Burst wave lithotripsy utilizes a series of focused sinusoidal ultrasound pulses to non-invasively fragment stones using a hand-held transducer. Effectiveness and safety in preclinical studies have been demonstrated, ^5–8 and two multi-institutional human clinical trials are just starting (NCT03873259 Intraoperative Assessment of Burst Wave Lithotripsy [BWL]; NCT03811171 Break Wave^TM Extracorporeal Lithotripter First-in-Human Study).

While much research remains to be done to define the optimal treatment parameters for ultrasonic propulsion and burst wave lithotripsy, we ultimately envision a single ambulatory-based ultrasound system that utilizes each of these technologies to optimally detect, move, and break stones in a non-invasive fashion in the clinic or acute setting. The optimal technology would allow sensitive and accurate detection of renal and ureteral stones, detachment of adherent stones, effective fragmentation of visualized stones, and directed movement of stones and stone fragments to facilitate stone comminution and fragment passage. Such a system may provide a novel, non-invasive approach to the diagnosis and management of stone disease while minimizing treatment cost and radiation exposure to patients.

Written by: Jessica C. Dai MD,¹ Michael R. Bailey Ph.D., MS,² Mathew D. Sorensen MD, MS,³ Jonathan D. Harper, MD.⁴

Author Affiliations:
1. Department of Urology, University of Washington, Seattle, Washington
2. Institute for Behavioral Medicine Research, Wexner Medical Center, Columbus, Ohio
3. Assistant Professor of Urology, Northwest Hospital & Medical Center, Seattle, Washington
4. Chief of Endourology and Minimally Invasive Surgery, University of Washington, Seattle, Washington

References:
1. Simon JC, Sapozhnikov OA, Kreider W, Breshock M, Williams JC, Bailey MR. The role of trapped bubbles in kidney stone detection with the color Doppler ultrasound twinkling artifact. Phys Med Biol. 2018;63(2):25011. doi:10.1088/1361-6560/aa9a2f
2. Dai JC, Dunmire B, Sternberg KM, et al. Retrospective comparison of measured stone size and posterior acoustic shadow width in clinical ultrasound images. World J Urol. 2018;36(5). doi:10.1007/s00345-017-2156-8
3. May P, Haider Y, Dunmire B, et al. Stone-Mode Ultrasound for Determining Renal Stone Size. J Endo. 2016;30(9):958-962.
4. Harper JD, Cunitz BW, Dunmire B, et al. First in Human Clinical Trial of Ultrasonic Propulsion of Kidney Stones. J Urol. 2016;195(4):956-964. doi:10.1016/j.juro.2015.10.131
5. Bailey M, Wang Y, Kreider W, et al. Update on clinical trials results of kidney stone repositioning and preclinical results of stone breaking with one ultrasound system. Proc Mtgs Acoust. 2018;35(020004). doi:https://doi.org/10.1121/2.0000949
6. Maxwell AD, Cunitz BW, Kreider W, et al. Fragmentation of Urinary Calculi In Vitro by Burst Wave Lithotripsy. J Urol. 2015;193(1):338-344. doi:10.1016/j.juro.2014.08.009
7. Wang Y-N, Krieder W, Hunter C, et al. Burst Wave Lithotripsy: An in vivo demonstration of efficacy and acute safety using a porcine model. In: 176th Meeting of the Acoustical Society of America. ; 2018.
8. Maxwell A, Wang Y, Kreider W, et al. Evaluation of renal stone comminution and injury by burst wave lithotripsy in a pig model. J Endourol. 2019. doi:10.1089/end.2018.0886

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