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    Ultrasound stone repositioning facilitates passage

    Technique also provides useful diagnostic information, researchers report


    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).

    Read: Alpha-blocker found safe in pregnant stone formers

    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.

    Also see: Is billing for stone prevention counseling possible?

    "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


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