So believes Shengcai Li, a Warwick University engineering professor, who is leading a team of researchers on the development of a new medical procedure that would use a carefully controlled, high-intensity focused ultrasonic beam (HIFU) to produce a cloud of bubbles around such stones to destroy them.
The technique mimics cavitation, a phenomenon that occurs around rotating equipment such as propellers in marine environments.
As a propeller rotates, it causes its surrounding liquid environment to drop below vapour pressure, leading to the formation of vapour bubbles.
ventually, these bubbles will flow into areas of water of higher pressure and collapse, releasing a damaging shock wave on the rotating equipment.
After years of studying ways to mitigate cavitation for the marine industry, Li came upon the idea of using the corrosive problem in the medical field.
The most appropriate application, he decided, was for gall, bladder and kidney stones. Some of the current procedures for removing troubling stones range from surgical removal to extra-corporeal shock wave lithotripsy (ECSWL), which uses ultrasound to generate short, sharp shocks in the body.
Li said ECSWL relies on cavitation to shake up stones to obliteration, but it is an unfocused treatment and risks damaging surrounding
tissues. He said: ’If we use it properly we can control the accuracy of cavitation within 1mm. Therefore, we only attack the stone, not the nearby tissues.’
Li’s technique would use two transducers: one for visualising the stones and the other for generating high-intensity ultrasonic beams.
The first beams generated into the patient’s body would create the low-pressure conditions needed to produce vapour bubbles in the urine surrounding the stones. Once a sufficient cloud of bubbles has formed around the stones, a second wave of beams would be directed into the body to collapse the bubbles around them.
In laboratory conditions, using a tank of water to represent urine and small chalk balls to represent stones, Li’s research team has destroyed stones within seconds.
Li said his team is looking to create better body simulations using layers of gelatin to mimic tissues and kidneys. He believes within two years his team will be ready for clinical trials, and commercialisation could follow in four years.
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