Industrial Physics Forum 2014: Sound surgery

The modern hospital operating room is full of high-tech gadgets, but the main tool a surgeon wields, the scalpel, is at least as old as the ancient Egyptians. But now physicists could help replace the surgeon’s knife with safer, noninvasive surgical methods, argues Lawrence Crum , a research professor in the Department of Bioengineering at the University of Washington.

In a Wednesday session of the Industrial Physics Forum , held in conjunction with the American Physical Society’s 2014 March meeting in Denver, Colorado, Crum described how focused sound waves can treat internal tissue without cutting through the skin.

Most people are familiar with diagnostic ultrasound, used famously by celebrities to capture pre-birth baby pictures, and more prosaically to image gallstones, cysts, blood vessels, and other body structures. To produce diagnostic ultrasound images, medical technicians coat the skin with a conductive gel and aim high frequency sound waves into the body. The waves reflect off internal body parts and bounce back into the ultrasound probe. A computer interprets the echoes and creates an image a doctor (or the tabloid press) can examine.

Ultrasound imaging has progressed greatly in the past few decades. But Crum focused his talk on a different dimension of ultrasound: as therapy to kill unwanted or malignant tissues in the body.

Diagnostic ultrasound uses very short pulses that won’t damage tissue, but longer, high intensity bursts of sound can heat the proteins inside cells until they lose their natural structure, a process called denaturing. (This is the same process evident in cooked eggs, incidentally.) High-intensity ultrasound pulses can also create acoustic cavitation in the body, a process in which tiny bubbles rapidly expand and then burst, generating concentrated pockets of thousand-degree heat and jets of fluid that eat away tissue.

“High-intensity ultrasound can cook tissue or can obliterate it in a matter of seconds,” Crum said. With such destructive power at their fingertips, medical researchers and doctors work hard to shoot the sound waves at only the diseased or unwanted parts of the body.

Therapeutic ultrasound devices focus sound waves in much the same way a magnifying glass might focus optical waves to start a fire. To make sure the high intensity beam is aimed at the proper internal body part, doctors currently use MRI machines or ultrasound imagers to monitor the heating of the tissue.

Crum listed successful clinical applications of therapeutic ultrasound to date, including treatment of tumors, fibroid masses, and misfiring neurons. He also touched on how ultrasound-induced cavitation might help open up the blood-brain barrier, allowing drugs to enter the brain to treat cancer and other brain diseases.

“I like to kid my daughter, an eye surgeon, that even the Romans had scalpels,” said Crum. “Ultrasound takes surgery to a new level.”

Catherine Meyers is science writer in the media services division of the American Institute of Physics.