Sound bites?

New research suggests a sound beam could be used as a scalpel in a non-invasive surgery technique

Sound Waves
Sound waves can be focused into small spot creating a scalpel for non-invasive surgery

We all heard of lasers. A similar concentration of sound has been achieved by engineering researchers

A carbon-nanotube-coated lens that converts light to sound can focus high-pressure sound waves to a fine degree as never before. The University of Michigan engineering researchers have developed a new therapeutic ultrasound approach indicating that it could lead to an invisible knife for non-invasive surgery.

Current ultrasound technology can offer us glimpses into the womb. But it is also used by doctors as focused sound waves to blast apart kidney stones and prostate tumours. The new technique works primarily by focusing sound waves tightly enough to generate heat, says Jay Guo, a professor of electrical engineering and computer science, mechanical engineering, and macromolecular science and engineering. Guo has co-authored the paper on this new technique that was published in the Nature's journal Scientific Reports.

The beams that today's technology generates can be bulky, says Hyoung Won Baac, a research fellow at Harvard Medical School who was part of this project as a doctoral student in Guo's lab.

"A major drawback of current strongly focused ultrasound technology is the big focal spot, which is of the order of several millimetres," Baac said. "A few centimeters is typical. Therefore, it can be difficult to treat tissue objects in a high-precision manner, for targeting delicate vasculature, thin tissue layer and cellular texture. We can enhance the focal accuracy 100-fold."

The team was able to concentrate high-amplitude sound waves to a spot just 75 by 400 micrometers [a micrometer is one-thousandth of a millimetre]. Their beam can blast and cut with pressure, rather than heat. Guo imagines that this technique may be able to do surgeries painlessly since its beam can so sharply focused that it can avoid nerve fibres. The device hasn't been tested in animals or humans yet, though.

"We believe this could be used as an invisible knife for non-invasive surgery," Guo said. "Nothing pokes into your body, just the ultrasound beam. And it is so tightly focused, you can disrupt individual cells."

Guo's team converted light from a pulsed laser to high-amplitude sound waves through a specially designed lens. The U-M researchers' system is unique because it performs three functions: it converts the light to sound, focuses it to a tiny spot and amplifies the sound waves. The sound waves are 10,000 times higher frequency than humans can hear. They work in tissues by creating shock waves and micro-bubbles that exert pressure toward the target, which Guo envisions could be tiny cancerous tumours, artery-clogging plaques or single cells to deliver drugs. The technique might also have applications in cosmetic surgery.

In experiments, the researchers demonstrated micro ultrasonic surgery, accurately detaching a single ovarian cancer cell and blasting a hole less than 150 micrometers in an artificial kidney stone in less than a minute.

"This is just the beginning," Guo said. "This work opens a way to probe cells or tissues in much smaller scale."

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