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Moving objects with ultrasound beams—potential application to urinary stone disease

Researchers have developed a noninvasive technology using ultrasound beams to lift and reposition an object in a living animal—an advance that could potentially be used to treat people with urinary stone disease. Urinary stones (also referred to as kidney stones) are one of the most common disorders of the urinary tract. Smaller stones may pass with little or no pain, while larger stones may get stuck along the lower urinary tract and block the flow of urine, causing severe pain and/or bleeding. Current treatments for urinary stones, such as lithotripsy that breaks stones into smaller pieces, may leave behind residual stone fragments. Most fragments will pass on their own, but others may grow larger, cause pain, and may require the need for additional treatment.

Working to advance safe, effective, and more efficient ways to reposition and encourage the passage of urinary stones, researchers have developed a noninvasive strategy to essentially trap a stone in an ultrasound beam (i.e., acoustic trapping). Trapped within this beam, the stone can be moved or repositioned by either moving the device that generates the ultrasound waves (e.g., transducer) or electronically steering the ultrasound beam by altering the phase of the wave. The scientists first demonstrated that the ultrasound beam could trap, lift, and steer a 3-millimeter glass sphere under ideal conditions—in a water tank. They moved the sphere a total distance of 6 millimeters vertically and 6 millimeters horizontally. The researchers further reported that this noninvasive acoustic trapping approach successfully moved glass spheres in the urinary bladders of three female pigs. To accomplish this, a single 3-millimeter glass sphere was placed in the bladder of each anesthetized animal using a tube with a camera-equipped scope and a device carrying the glass sphere. The camera monitored the sphere movement and was used to evaluate changes to the bladder wall after each acoustic trapping manipulation. Importantly, the technology did not cause detectable injury to the animals’ bladder wall.

This study demonstrates the ability to manipulate objects in the pig bladder using acoustic trapping, with potential application to treating urinary stones as well as other medical uses. Future research will be needed to evaluate the safety and effectiveness of this approach with respect to variations in shape, structure, and composition of urinary stones along the entirety of the urinary system, as well as to determine if it could be used in people. The technology associated with this translational work has been licensed to a small business.

Ghanem MA, Maxwell AD, Wang Y-N,…Bailey MR. Noninvasive acoustic manipulation of objects in a living body. Proc Natl Acad Sci USA 117: 16848-16855, 2020.

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