Nearly 1 in 10 people will someday experience a kidney stone, which creates what is described as the most intense pain imaginable. However, a new device developed at the University of Washington (UW) in Seattle would let doctors use ultrasound to move kidney stones inside the body to help them pass naturally.
“Ultrasound is used today to break up large stones. That’s not what we’re doing,” explains Michael Bailey, an engineer at the UW Applied Physics Laboratory. “We’ve developed low-power ultrasound that could move small stones to reduce pain, expense, and treatment times.”
Kidney stones are crystals that develop in urine. Shock-wave ultrasound has been used to treat big kidney stones for 30 years. That technique, known as lithotripsy, sends short pulses of high-energy ultrasound to shatter large stones. While non-invasive, the technique usually requires general anesthesia and a hospital visit. It also leaves behind fragments that can grow and require another trip to the hospital or emergency room.
A patient with a small stone traditionally has to wait, drink plenty of water, and hope that the stone passes uneventfully. Medical studies have looked at standing on your head or hitting the patient in the lower back (technically called inversion and percussion). Those methods try to jiggle small stones from the lower part of the kidney, where they have only a 35% chance of passing naturally, to the middle of the kidney, where they have an 80% chance of passing without treatment.
The UW team proposes a gentler, more targeted way to guide the stones toward the exit route.
The prototype is a commercial ultrasound system modified to emit pulses only slightly stronger than those used for pregnancy imaging. These sustained, low-intensity waves are just enough to push the crystal through the surrounding fluid.
In the lab, Barbrina Dunmire, an engineer at the Applied Physics Laboratory who helped build the device, points an ultrasound probe at a stone inside a latex kidney. She activates the ultrasonic pulse and the stone immediately swings away through the clear liquid. A doctor would put the probe on a patient’s lower back, then use an onscreen ultrasound image to locate the stone and direct it with the ultrasonic pulse.
Urologists and urology residents at UW Medicine tested three successive prototypes on artificial kidneys and pigs, and helped to design the touchscreen user interface. Currently, there is a 15-patient human trial using this technology.
“We’ve had extensive testing in an animal model,” says Dr. Jonathan Harper, an assistant professor of urology at UW Medicine. “If it acts in the same way in a human kidney, I think it’s extremely promising.”
Besides guiding kidney stones to help them pass naturally, other applications could be to reposition a stone before or during surgery; to displace a large stone obstructing the ureter to relieve the patient’s pain and avoid emergency surgery; and perhaps someday to escort small stones right down the ureter.
The team is working with the UW Center for Commercialization. Once the UW team has proven the technique works in humans, Bailey says, the project will be ready to seek FDA clearance and be brought to market.
University of Washington
The research is supported by the National Institutes of Health and the National Space Biomedical Research Institute. This was adapted from a press release from the University of Washington Applied Physics Laboratory.