Ultrasound stone repositioning facilitates passage

New Orleans-The first clinical trial of a novel ultrasound technology shows that it can safely reposition stones in situ to make them more amenable to natural passage and treatment.

Dr. HarperThe approach can also provide useful diagnostic information in distinguishing a larger stone that would not pass from a cluster of much smaller, passable stones, according to the study's authors.  

"We have completed the first clinical trial of this technology in 15 patients and have met the goals of the study. The primary goal was to demonstrate that we could move stones within the kidney in humans. We did that in 14 of 15 patients. Secondary goals were also achieved in that it was tolerated in the clinic setting without pain, and there were no adverse events related to the procedure," first author Jonathan Harper, MD, associate professor of urology at the University of Washington, Seattle, told Urology Times.

"By repositioning stones, we were able to facilitate stone passage in four of the six post-lithotripsy patients," he said.

NEXT: Acoustic radiation force of ultrasound waves transcutaneously moves stones within the kidney

Dr. Harper described the technology developed by the Washington team as a new application of ultrasound that uses the acoustic radiation force of ultrasound waves to transcutaneously move stones within the kidney. The trial, which was presented at the AUA annual meeting in New Orleans, initially involved 13 awake, non-anesthetized patients selected without restriction of body habitus, stone size, or stone location. An additional two patients were incorporated in the study to gain more knowledge of stone repositioning by direct visualization of stone movement during ureteroscopy. This has led the group toward more optimized treatment parameters.

The majority (11) of the 15 patients were men, average age 56 (+/–11) years, and average body mass index was 29.3 kg/m² (+/–3.1). Stone sizes ranged from 1 mm to 14 mm and were located in the lower pole (24), interpolar (10), upper pole (four), and renal pelvis/ureteropelvic junction (four).

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Stones were successfully relocated in all six post-lithotripsy patients, four of whom passed more than 30 fragments in the days following the procedure. One subject passed two 2-mm fragments before leaving the clinic.

An unanticipated finding

One finding that was unanticipated was that in four patients, a stone that appeared to be greater than 5 mm on imaging was visually confirmed to be a composite of smaller, passable stones with repositioning.

The technology described by Dr. Harper is innovative.

"The probe we used in the trial is a standard, off-the-shelf ultrasound transducer in terms of imaging capabilities, but the ultrasonic propulsion technology is completely new and innovative. There is no published data outside our work describing this technology or its application,” said Dr. Harper, who noted that it was developed in conjunction with the University of Washington's Applied Physics Laboratory.

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"The imaging and ultrasonic propulsion are incorporated into the device for real-time feedback. The probe is used for imaging at one setting, and a different setting allows for propulsion or repositioning. The way the ultrasound is delivered is completely different than standard imaging. We have a clinical prototype, and we have had success with our first 15 patients.

“Given the results of the clinical trial, there is a role for this technology in its current state, but we think we can make it better. Some of the new (probe) designs that have been developed over the past few weeks suggest it may have broader applications, whether these are moving a clump of fragments, detaching a small stone, or repositioning a larger obstructing stone," he said.

NEXT: Learning curve to technology

Learning curve to technology

Moving stones using the technology is not as simple as shooting pool.

"There is a learning curve to this technology. You have to be able to use renal ultrasound and visualize the path you want to move the stone. If you are aiming into a wall, the stone is not going to go anywhere. It can take some trial and error to move the stones," Dr. Harper said.

The finding that a larger stone was actually a collection of smaller stones or fragments turned out to be a diagnostic advantage that was unanticipated. Such findings can lead to revisions of clinical management, Dr. Harper said.

The study was funded by the National Space Biomedical Research Institute, a division of NASA, and the National Institutes of Health.

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