Presentation Authors: Adam Maxwell*, Yak-Nam Wang, Wayne Kreider, Bryan Cunitz, Frank Starr, Donghoon Lee, Yasser Nazari, Seattle, WA, James Williams, Indianapolis, IN, Michael Bailey, Mathew Sorensen, Seattle, WA
Introduction: Burst wave lithotripsy (BWL) is a preclinical method developed to noninvasively fragment kidney stones with low-amplitude focused bursts of ultrasound. In this study, we assessed the effectiveness of stone fragmentation with specific ultrasound parameters and the acute bioeffects of the same exposures to the kidney in a clinical simulation of BWL.
Methods: A 6-7 mm natural human kidney stone composed of calcium oxalate monohydrate was implanted surgically in each kidney of three pigs weighing 70-80 kg each. A 350-kHz burst wave lithotripsy focused ultrasound transducer was coupled to the animal by a water bath placed on the flank. Real-time image guidance was performed by an inline ultrasound imaging probe used to identify and target the stone, as well as monitor for echogenicity indicative of cavitation that may produce injury. Each stone was exposed for 30 minutes to BWL bursts with amplitude of 7 MPa focal pressure at a pulse rate of 10 Hz and a burst duration of 20 cycles. If any echogenicity was observed via imaging during treatment, the applied focal pressure was reduced to 6.5 MPa and exposure was continued for the remainder of the 30 minutes. After treatment, the kidneys were extracted for gross and histologic assessment, as well as MRI analysis. The stone fragments were retrieved and the remaining mass of fragments >2 mm after treatment were compared to the initial mass to determine the fragmentation effectiveness.
Results: In 3 of 5 cases stones were reduced completely to fragments < 2 mm. On average, 82% Â± 22% of the stone mass was reduced to fragments < 2 mm with all treatments resulting in â‰¥58% of mass fragmented. One stone was not treated because no suitable acoustic window could be found. Hyperechoic areas were briefly detected in kidney in two treatments, but were not observed after reducing the pressure amplitude to 6.5 MPa. No detectable injury was found in the parenchymal tissue of any kidney by gross, MRI, or histologic examination, although petechial damage and erosion were identified to the urothelium of the collecting system limited to the area directly around the stone.
Conclusions: Burst wave lithotripsy can produce consistent stone fragmentation with use of appropriate ultrasound parameters. Such exposures cause minimal injury to the kidney and urinary tract during treatment.
Source of Funding: Work supported by NIH NIDDK grants DK043881 and DK104854, and resources from the VA Puget Sound Health Care System.