MRI, ultrasound detect post-burst wave lithotripsy injury

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Researchers who are investigating burst-wave lithotripsy, a potential alternative treatment for kidney stones, report that magnetic resonance imaging and ultrasound scans hold promise as tools to help scientists analyze related kidney injuries.

San Diego-Researchers who are investigating burst-wave lithotripsy, a potential alternative treatment for kidney stones, report that magnetic resonance imaging and ultrasound scans hold promise as tools to help scientists analyze related kidney injuries.

"MRI can identify hemorrhagic injury caused by burst-wave lithotripsy and is a useful tool to quantify this injury. Ultrasound imaging may provide a real-time method to detect the onset of injury during lithotripsy and could be useful in monitoring lithotripsy procedures,” said lead author Adam Maxwell, PhD, acting assistant professor in urology at the University of Washington, Seattle.

At the moment, burst-wave lithotripsy is in the preclinical stage.

"It is similar to shock wave lithotripsy, which is used clinically, but emits lower-amplitude pulses of ultrasound instead of shocks," Dr. Maxwell told Urology Times. "This difference results in characteristics unique to burst-wave lithotripsy. For instance, we can control the size of fragments that a stone breaks into by changing the ultrasound frequency. This may let us break a stone into exclusively small fragments that would spontaneously and asymptomatically pass."

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According to Dr. Maxwell, the authors hope that burst-wave lithotripsy will become a first-treatment for stones instead of shock-wave lithotripsy or ureteroscopy.

"We are working toward making a system that is entirely ultrasound-based, both for therapy and image guidance," he said. "Potentially, it could be an office-based procedure."

As research continues, Dr. Maxwell said he and his colleagues have been looking for an alternative to the standard morphometric method that is used in shock wave lithotripsy research. "It requires a high level of expertise and is very time-consuming," he said.

Enter the potential use of MRI and ultrasound scans as an alternative. Dr. Maxwell and colleagues examined both technologies in pigs and reported their findings at the 2016 AUA annual meeting in San Diego.

Next: Imaging compared to morphometric analysis

Imaging compared to morphometric analysis

In regard to ultrasound, the authors tested the technology on 21 sites in four pigs during treatment. The authors report that detection of cavitation via ultrasound was consistent with the presence or absence of injury, as shown via MRI, in 20 of 24 sites and consistent with morphometric analysis in all but one of 15 sites. Lesions identified via MRI, meanwhile, were consistent with morphometric analysis in 13 of 15 sites.

Ultrasound imaging, especially Doppler, is sensitive to cavitation bubbles caused by burst-wave lithotripsy, Dr. Maxwell said.

"We hypothesize that injury occurs when and where these bubbles form in tissue. We detected cavitation on ultrasound exclusively during exposures where injury was found using the standard method,” he said.

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As for MRI scans, identified lesions coincided with morphometric analysis in 13 of 15 sites.

"We identified sequences that could sensitively and specifically detect hemorrhagic injury in fixed kidneys, although there is some discrepancy between methods in the measured size of the lesion," Dr. Maxwell said.

What's next? "Using these imaging methods, our next goals are to perform more extensive safety studies and quantify injury with burst-wave lithotripsy exposures that could potentially be used in a clinical setting," Dr. Maxwell said. "We also plan to develop and test our ultrasound imaging methods to provide feedback to detect the onset of injury and perhaps control exposures based on this feedback in real time."

Dr. Maxwell has an investment interest and consultant/adviser role with SonoMotion, a medical device company that is exploring kidney stone treatments.