Good vibrations: Heart tissue from a pig that has been zapped by ultrasound pulses. The untreated cells are still intact, while the treated tissue (lower left) is completely liquefied.

Credit: J. E. Parsons et al, Ultrasound in Med. & Biol.

Related articles

• Mouse study shows ultrasound affecting brain development
• Australian research breakthrough in growing human organs
• Smile! A new Canadian tool can re-grow teeth say inventors
• Ultrasound could help explore watery moon
• New stem cells can make heart muscle

NEW YORK: With some modification, the same ultrasound technology that allows parents to see their children in the womb could one day allow surgeons to operate inside the body without making a single cut.

The technique, called 'histotripsy,' is being developed by biomedical engineer Charles Cain and his team at the University of Michigan in the U.S., and was detailed this week at the Acoustical Society of America meeting in New Orleans, Louisiana.

Bursting microbubbles

Histotripsy uses pulses of ultrasonic frequency sound waves to break down diseased or unwanted tissue inside the body. The ultrasound used is hundreds of times more powerful than that used for imaging and – like sunlight through a magnifying glass – can be focused into narrow beams only a few millimetres wide.

With a magnifying glass "you can focus the light waves into a focal point, and if you put paper there, you can set it on fire," said study team member Zhen Xu. "But you are not going to set fire [to the space] in between." Histotripsy works in a similar way, meaning that the ultrasound pulses can target cells located deep inside the body without damaging intervening tissue, she said.

The beams create 'microbubbles' in the fluid of the target tissue that rapidly swell and collapse in a process called cavitation. The collapsing microbubbles release large amounts of energy and function as "miniscapels" to liquefy the tissue, said the researchers. The small amount of resulting cellular slurry is reabsorbed and recycled by the body.

Lasers can already be tapered into beams narrower than ultrasound, but they generate so much heat that they can't penetrate more than a few millimetres of tissue without causing collateral damage, said Zhen. "[But] using ultrasound, we can penetrate several centimetres."

Exciting new technique

Another major advantage of histotripsy over other techniques, such as radiation or thermal therapies, is that doctors can monitor the surgery in real time, because the microbubbles show up clearly in conventional ultrasound images and MRI imaging. Controlling and manoeuvring the beams is also easy with a computer mouse or joystick.

John Cheatham, co-director of the U.S. Heart Centre at Nationwide Children's Hospital in Columbus, Ohio, commented that the exciting new technique has a lot of potential for non-invasive surgery.

"In my world of cardiology, the non-invasive creation of holes in desired locations within the beating heart will be possible without a scalpel or catheter," said Cheatham. "We believe this new technology will revolutionise certain aspects of medicine and bring us into a new era."

Zhen and her colleagues are currently testing histotripsy in animals and hope to move onto clinical trials with humans in a few years.