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UW team tests technologies to roll kidney stones and crumble them
(2016-03-15)
Two new technologies developed by University of
Washington researchers could bring noninvasive
relief to such patients.
Expelling the stones.
The first technology uses ultrasound to move kidney
stones inside the body and help them pass naturally
through the ureter.
A lot of people have smaller stones that would pass
on their own, but sometimes the stones just sit in
the kidney. They can eventually regrow into a larger
stone or can pass at an inopportune time and cause a
lot of pain,” said Adam Maxwell, a UW acting
assistant professor of urology. “Ultrasonic
propulsion is used to expel these fragments in a
controlled manner. Our hope is that this technology
will prevent people from getting recurring stones.”
The prototype device is a diagnostic ultrasound
imager reconfigured to emit pulses that are longer
and slightly stronger than those used for pregnancy
imaging. Physicians can view and push the stones
simultaneously. They can reposition stones before
surgery and dislodge larger stones that obstruct the
ureter.
The device is being tested in two clinical trials.
The first extends a trial in which no adverse
effects were experienced by the initial 15
participants. All were awake during the procedure;
two felt some sensation in the kidney but not enough
to halt the procedure.
Based on those results, the Food and Drug
Administration recently approved adding 15 more
participants.
A second trial aims to help patients who come to the
hospital with acute kidney stone pain. “The trial
will use ultrasonic propulsion in the emergency
department to dislodge or slightly move the stones
or help patients pass the stone to relieve pain and
pressure. Ultimately, we want to try to avoid an
emergency surgery or at least take the patient out
of discomfort,” said Michael Bailey, principal
engineer in UW’s Applied Physics Lab.
Burst wave lithotripsy uses focused ultrasound to
crumble stones into uniform, small fragments,
allowing the stones to pass naturally.
The idea originated from 20 years of research of
shock wave lithotripsy, in which shock waves are
used to break up kidney stones. Maxwell and Bailey
found that short ultrasound pulses actually broke
stones faster and into smaller pieces than shock
waves.
The challenge for researchers is to find the optimal
frequency to break the stones into fragments small
enough to pass, Maxwell explained. At the lowest
frequency they have tested, certain stones can be
broken into large fragments in seconds. The highest
frequency can break a similar stone into sand-sized
particles in 10 to 20 minutes (compared with 30 to
60 minutes for shock wave lithotripsy).
In lab feasibility studies, burst wave lithotripsy
has broken “just about every type of natural stone,”
Maxwell said. And in animal studies, the team has
found a safe range of pressure that breaks stones
and does not cause injury.
The system being developed will be smaller and more
portable than shock wave lithotripsy machines,
potentially making it an office-based procedure, he
added. “Rather than needing to go to the operating
room, the physician could have the device in the
office and try to break a patient’s stones as the
first line of therapy.”
Burst wave lithotripsy is still in the preclinical
stage. The team hopes that in a couple years they
can move into a clinical trial, and, ultimately,
give patients and physicians another choice in the
treatment of kidney stones.
For more information
University of Washington Link...
