Ultrasonic ‘tweezers’ can remove huge kidney stones without invasive surgery

Kidney stones can be horrendously painful. Caused by a buildup of waste products in the blood, they’re spiky crystals that form together to create a stone-like mass inside the kidneys. While smaller ones may be passed with urine, larger kidney stones can become stuck inside the kidneys or in the narrow tube connecting the kidneys to the bladder. In some cases, invasive surgery is the only answer for removing them.

But scientists are working to change that. A team of scientists led by the University of Washington in Seattle have developed a new, high-tech removal approach best described as “ultrasound tweezers.” It would allow ultrasound beams to get rid of kidney stones in patients by literally steering them out of the body.

This is achieved using something called radiation force, an increasingly promising optics phenomena. “[For an example,] think about a spaceship that opens its sails in space to absorb the sun’s radiation and propel it forward,” Mohamed Ghanem, a postdoctoral scholar at the University of Washington, told Digital Trends.

In 2018, the Nobel Prize in Physics was awarded to Arthur Ashkin for a radiation force demonstration in which a focused laser beam was used to trap micron-sized particles. In this new study, soundwaves are instead used to impart radiation forces to trap and manipulate objects, with an acoustic beam grabbing and maneuvering them in 3D space.

“We used a multi-element array to create acoustic beams that can trap large objects by controlling the delays between the acoustic emission of each element,” Ghanem explained. “We experimentally measured the radiation forces on millimeter-sized dense objects to confirm the theoretical modeling with our acoustic output.”

While the approach hasn’t yet been demonstrated in humans with real kidney stones, the researchers have showcased that the technique can accurately move and steer tiny glass beads along a predefined course in the bladder of a live pig. This process was monitored using an ultrasound imaging probe.

“Our work shows the ability to manipulate large objects in the living body at acoustic power exposure that are safe for the surrounding tissue,” Ghanem said. “Our next step is to generalize the work for actual kidney stones that are varying in shape, structure, and composition, and to perform the manipulation in the kidney. This will pave the way for many other medical and non-medical applications, such as manipulation of surgical instruments in the body or zero-contamination laboratory application.”

The technology has been licensed to the U.S. firm SonoMotion. A paper describing the research was recently published in the journal PNAS.

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