Focused ultrasound, for decades, has held the promise of high precision surgery without incision. Yet it has remained limited to things like breaking up kidney stones and destroying uterine fibroids. It’s been difficult to create a high energy beam narrow enough for more precise applications.
Researchers at the University of Michigan may have come up with a solution, using an optoacoustic method of generating sound waves from a laser source. The technique has allowed them to reduce the size of the focal point about 100 fold to an effective area of 75 by 400 micrometers. The team believes this technique can open up a new world of minimally invasive surgery, which will probably be helped by intra-operative MRI or ultrasound for real time guidance.
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. To achieve the amplification, the researchers coated their lens with a layer of carbon nanotubes and a layer of a rubbery material called polydimethylsiloxane. The carbon nanotube layer absorbs the light and generates heat from it. Then the rubbery layer, which expands when exposed to heat, drastically boosts the signal by the rapid thermal expansion.
The resulting sound waves are 10,000 times higher frequency than humans can hear. They work in tissues by creating shockwaves and microbubbles that exert pressure toward the target, which Guo envisions could be tiny cancerous tumors, 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.
Press release: Super-fine sound beam could one day be an invisible scalpel
Open access article in Scientific Reports: Carbon-Nanotube Optoacoustic Lens for Focused Ultrasound Generation and High-Precision Targeted Therapy