Exploding Bubbles Trim The Prostate

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In the traditional treatment for prostate growths, a rigid instrument is inserted through the penis and used to scrape away cells lining the walnut-sized gland. Urologist William Roberts and a team at the University of Michigan, Ann Arbor, are developing a less invasive way to remove tissue using focused pulses of ultrasound. Their technique, histotripsy, has now been used to safely trim the interiors of aging prostates in the body.

Unlike other therapeutic ultrasound technologies in development, which create heat to boil pathogenic tissue, histotripsy mechanically breaks apart tissue with shorter, strong pulses of ultrasound. These pulses create tiny bubbles out of dissolved gas in prostate tissue. As the bubbles violently collapse, they release tiny shock waves, a phenomena called acoustic cavitation. Over tens of thousands of pulses, the combined force of these cavitations liquefies nearby tissue into slurry that is eliminated through the urine. This tissue excavation can be monitored and targeted in real time with acoustic imaging.

"Historically, no one believed that cavitation could be controlled like this. We're the only group doing this kind of work," says Roberts. His team used the technique to dissolve marble-sized chunks of cells in the walls of prostates. Side effects common in traditional prostrate treatments -- bleeding and inflammation -- were minimal after histotripsy treatment, as were signs of discomfort. Roberts hopes to develop histotripsy into a clinical treatment for early-stage cancer and enlarged prostate (BPH).

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