Sound as a Scalpel

File this one under Totally Awesome.


Medical researchers have developed a way to use ultrasound to do non invasive brain surgery. Yep, brain surgery with no skull cracking or icky blood. The science behind the technique is actually quite simple. Ultrasound is a term for sound waves which are above the range of human hearing. You might not think about it often, but sound is comprised of waves of pressure traveling through a medium, usually air, with a frequency our ear is tuned to receive (12 Hz to 20kHz). Ultrasound is most commonly know for its use in imaging fetuses in utero, which it does by emitting high frequency pressure waves and then measuring the reflection when the sound reflects off the fetus. The reflections occur because different parts of the body, including the fetus, have different densities. The same principle is used by whales to navigate and by you when calling out in the mountains to hear your echo reflected off the peaks.

Now we need to go from the gentle imaging of a fetus to the destructive procedure of brain surgery and to do this we have to understand the physics of sound. As I mentioned above, sound is a pressure wave traveling through a medium, and a pressure wave is a series of compressions and rarefactions of that medium. As it travels the wave looses energy by transferring kinetic energy to the material it passes through. The kinetic energy then results in heating. A single beam of ultrasound will not result in much heating, so we don't have to worry about frying junior. However, the high intensity focused ultrasound used in the non invasive brain surgery focuses up to 100 beams of ultrasound onto the diseased spot of the brain, delivering enough energy to destroy the tissue. And there is no need for anesthesia in this outpatient procedure. Pretty awesome, huh? Sign me up!..uh...well...sign me up if I ever need it.

This technique is also being developed for treating various forms of cancer, such as breast cancer, as well as Parkinson's disease, and has great potential. It's a lovely example of how a little physics know-how can provide powerful insight and opportunity.