Ramesh S. et al., 2020: In Vitro Evaluation of Urinary Stone Comminution with a Clinical Burst Wave Lithotripsy System
Ramesh S, Chen TT, Maxwell AD, Cunitz BW, Dunmire B, Thiel J, Williams JC, Gardner A, Liu Z, Metzler I, Harper JD, Sorensen MD, Bailey MR.
Applied Physics Laboratory, Center for Industrial and Medical Ultrasound, University of Washington, Seattle, Washington.
Department of Urology, University of Washington School of Medicine, Seattle, Washington.
Department of Anatomy, Cell Biology and Physiology and Indiana University School of Medicine, Indianapolis, Indiana.
Department of Biostatistics, Indiana University School of Medicine, Indianapolis, Indiana.
Division of Urology, VA Puget Sound Health Care System, Seattle, Washington.
OBJECTIVE: Our goals were to validate stone comminution with an investigational burst wave lithotripsy (BWL) system in patient-relevant conditions and to evaluate the use of ultrasonic propulsion to move a stone or fragments to aid in observing the treatment endpoint.
MATERIALS AND METHODS: The Propulse-1 system, used in clinical trials of ultrasonic propulsion and upgraded for BWL trials, was used to fragment 46 human stones (5-7 mm) in either a 15-mm or 4-mm diameter calix phantom in water at either 50% or 75% dissolved oxygen level. Stones were paired by size and composition, and exposed to 20-cycle, 390-kHz bursts at 6-MPa peak negative pressure (PNP) and 13-Hz pulse repetition frequency (PRF) or 7-MPa PNP and 6.5-Hz PRF. Stones were exposed in 5-minute increments and sieved, with fragments >2 mm weighed and returned for additional treatment. Effectiveness for pairs of conditions was compared statistically within a framework of survival data analysis for interval censored data. Three reviewers blinded to the experimental conditions scored ultrasound imaging videos for degree of fragmentation based on stone response to ultrasonic propulsion.
RESULTS: Overall, 89% (41/46) and 70% (32/46) of human stones were fully comminuted within 30 and 10 minutes, respectively. Fragments remained after 30 minutes in 4% (1/28) of calcium oxalate monohydrate stones and 40% (4/10) of brushite stones. There were no statistically significant differences in comminution time between the two output settings (p = 0.44), the two dissolved oxygen levels (p = 0.65), or the two calyx diameters (p = 0.58). Inter-rater correlation on endpoint detection was substantial (Fleiss' kappa = 0.638, p < 0.0001), with individual reviewer sensitivities of 95%, 86%, and 100%.
CONCLUSIONS: Eighty-nine percent of human stones were comminuted with a clinical BWL system within 30 minutes under conditions intended to reflect conditions in vivo. The results demonstrate the advantage of using ultrasonic propulsion to disperse fragments when making a visual determination of breakage endpoint from the real-time ultrasound image.
J Endourol. 2020 Mar 20. doi: 10.1089/end.2019.0873. [Epub ahead of print].
This is a fascinating report on the progress of a true third generation extracorporeal lithotripsy technique and therefore a must read.
An abstract published in 2017 [Reference 8 in the article (1)] tells a little bit different story: “At least 3 stones were treated for each condition, with fragmentation defined as percent stone mass and 13±2% breakage in basket, PVC, and anatomic phantoms, respectively”
But still you should definitely read it.
I do not precisely remember the details of a discussion 5 years ago with Dr. Wess about the loss of burst wave energy during passage through a human body and temperature elevation in the focal area. I will ask him for a comment.
1 Ahn J, Kreider W, Hunter C, et al. Improving environmental and stone factors toward a more realistic in vitro lithotripsy model. J Acoust Soc Am 2017;141:3673
See also Chen TT, Samson PC, Sorensen MD, Bailey MR. Burst wave lithotripsy and acoustic manipulation of stones. Curr Opin Urol. 2020 Mar;30(2):149-156. doi: 10.1097/MOU.0000000000000727.
The wish to fragmentize all types of human kidney and ureteral stones to small particles of cation is reasonable. Conventional shock wave lithotripsy (SWL) is doing a good job but there is still potential for improvements. New and more efficient fragmentation mechanisms and new device concepts are most welcome. A clinically qualified lithotripter has to include an efficient and safe therapy source, an ergonomic patient handling and targeting system and means to judge the status of fragmentation and the end of the treatment. The group of authors have all this in mind, have followed this ambitiously for several years and report progress as in this paper.
The final goal of their laborious efforts is to build an office based lithotripsy device, which provides live images of the treatment area (kidney stones), performs superior fragmentation to dust and small particles, has an integrated ultrasound propulsions system for repositioning stones/fragments to improve fragmentation efficiency and facilitate natural passage out of the patient’s body.
Alternatively, to the well-established shock wave technology the authors back on the technique of burst wave lithotripsy (BWL), which deems to deliver smaller fragments compared to shock wave lithotripsy.
The results presented are promising under laboratory conditions. There are many questions, however, to be addressed before clinical applications become routine:
• Is there enough comminution power to treat stones deep (≥ 10cm) in a patient’s body?
• Can the requested power stay below the threshold of cavitation without affecting fragmentation efficiency?
• Can the deposition of heat at the coupling surface and within the focal zone be limited without affecting fragmentation efficiency?
• What are the results with hard or larger stones (≥ 7mm)?
• What is if small fragments stay around the stones during comminution even if ultrasound propulsion may have moved the fragments?
The answers to these and other questions are mandatory to compete with or outrange conventional shock wave lithotripsy.
An interesting issue of the device is the implementation of sonographic B-mode imaging. Compared to fluoroscopic imaging this targeting modality has the advantage of life view of the treatment area and the possibility to judge (to a certain degree) the fragmentation process continuously.
The benefits of ultrasound imaging led to the development of different lithotripter concepts based on sonographic targeting (e.g. MODULITH SLK, Storz Medical). They had modest success in America since compared to fluoroscopy, reading sonographic images was not popular in the community of urologists.
Nevertheless, using real time ultrasound imaging may help to improve the hit rate of treatment pulses by continues visual observation and correction of the target location. This is necessary since slight movements of the target stone may shift the stone and its ultrasound echo out of the thin imaging plane of a B-mode picture.
• Regarding the possibility of moving stones and fragments by ultrasonic propulsion technique it may be of interest, that conventional shock waves application has an inherent feature of shock wave propulsion. This is due to the fact, that shock wave fragmentation is based on the mechanism of momentum transfer, which is responsible for the generation of forces that are mandatory for fragmentation see:
• Original Paper
• Open Access
• Published: 06 December 2018
Fragmentation of brittle material by shock wave lithotripsy. Momentum transfer and inertia: a novel view on fragmentation mechanisms
• Othmar J. Wess &
• Juergen Mayer
Urolithiasis volume 48, pages137–149(2020) Cite this article
• 1362 Accesses
Shock waves carry a momentum that is transferred from the shock wave to the fragments by reflection. According to Newton’s law of motion F= ma the forces can move stones and fragments out of their resting positions similar to ultrasound propulsion.
The paper of Ramesh et al. should stimulate further discussion.