May PC et al, 2017: Detection and Evaluation of Renal Injury in Burst Wave Lithotripsy Using Ultrasound and Magnetic Resonance Imaging.
May PC, Kreider W, Maxwell AD, Wang YN, Cunitz BW, Blomgren PM, Johnson CD, Park JSH, Bailey MR, Lee D, Harper JD, Sorensen MD.
University of Washington Applied Physics Lab, Center for Industrial and Medical Ultrasound, Seattle, Washington.
Department of Urology, University of Washington School of Medicine, Seattle, Washington.
Department of Anatomy and Cell Biology, Indiana University, Indianapolis, Indiana.
Department of Radiology, University of Washington, Seattle, Washington.
Division of Urology, Department of Veteran Affairs Medical Center, Seattle, Washington.
PURPOSE: Burst wave lithotripsy (BWL) is a transcutaneous technique with potential to safely and effectively fragment renal stones. Preclinical investigations of BWL require the assessment of potential renal injury. This study evaluates the capabilities of real-time ultrasound and MRI to detect and evaluate BWL injury that was induced in porcine kidneys.
MATERIALS AND METHODS: Ten kidneys from five female farm pigs were treated with either a 170 or 335 kHz BWL transducer using variable treatment parameters and monitored in real-time with ultrasound. Eight kidneys were perfusion fixed and scanned with a 3-Tesla MRI scanner (T1-weighted, T2-weighted, and susceptibility-weighted imaging), followed by processing via an established histomorphometric technique for injury quantification. In addition, two kidneys were separately evaluated for histologic characterization of injury quality.
RESULTS: Observed B-mode hyperechoes on ultrasound consistent with cavitation predicted the presence of BWL-induced renal injury with a sensitivity and specificity of 100% in comparison to the histomorphometric technique. Similarly, MRI detected renal injury with a sensitivity of 90% and specificity of 100% and was able to identify the scale of lesion volumes. The injuries purposefully generated with BWL were histologically similar to those formed by shock wave lithotripsy.
CONCLUSIONS: BWL-induced renal injury can be detected with a high degree of sensitivity and specificity by real-time ultrasound and post-treatment ex vivo MRI. No injury occurred in this study without cavitation detected on ultrasound. Such capabilities for injury detection and lesion volume quantification on MRI can be used for preclinical testing of BWL.
J Endourol. 2017 Jun 16. doi: 10.1089/end.2017.0202. [Epub ahead of print]. FREE ARTICLE
An important study because it reports on work in progress on an ESWL technique alternative to classical ESWL. It requires careful reading.
The experimental setting is exceptional: “The purpose of this study was to develop imaging techniques for assessing BWL-induced renal injury in a porcine model.” “Due to geometric constraints of available BWL transducers as well as a desire to deliver repeatable, known pressures to targeted sites, intra-abdominal treatments were performed. Animals were placed supine and a mid-line incision was made to gain access to the kidneys. The abdominal cavity was filled with degassed phosphate buffered saline solution before coupling the BWL treatment probe directly to the anterior surface of the exposed renal capsule for treatment.“
“Each kidney was treated in three sites: upper, middle, and lower poles, which were identified using US visualization of the renal pelvis as a landmark. BWL exposures up to 30 minutes were delivered using bursts with amplitudes from 5.8 to 8.1 MPa with a pulse length of 10 cycles at 170 kHz or 20 cycles at 335 kHz. A burst repetition rate of 40 Hz was used for all treatments at 335 kHz; for several treatments at 170 kHz, a burst repetition rate of 200 Hz was used.”
The authors show that hyperechogenitiy in the real time ultrasound image observed during BW exposure reliably signifies tissue trauma seen later on in MRI-images.
“This result suggests US should serve as a real-time method to monitor for cavitation to prevent renal injury during BWL treatment. If cavitation is detected the user could pause the treatment to allow the cavitation bubbles to clear before further treatment at the same or a reduced output level.” This is somehow inconsequent as the ultrasound image proves the trauma that has already happened. The authors also do not report if the lesions seen were quantitavely related to the time of exposure or the amount of energy transmitted. “Despite deliberate exposure of tissues to sustained cavitation during BWL treatment exposures, most of the acute hemorrhagic injury in this study was th shock wave application to kidneys. It is not yet well understood why and when parenchymal side effects happen.