Recording Brain Activity with Laser Light

A Caltech professor, in collaboration with researchers at the University of Southern California, has demonstrated for the first time a new technology for imaging the human brain using laser light and ultrasonic sound waves.

The technology, known as photoacoustic computerized tomography, or PACT, has been developed by Lihong Wang, Bren Professor of Medical Engineering and Electrical Engineering, as a method for imaging tissues and organs. Previous versions of the PACT technology have been shown capable of imaging the inner structures of a rat's body; PACT is also capable of detecting tumors in human breasts, making it a possible alternative to mammograms.

Now, Wang has made further improvements to the technology that make it so precise and sensitive that it can detect even minute changes in the amount of blood traveling through very tiny blood vessels as well as the oxygenation level of that blood. Since blood flow increases to specific areas of the brain during cognitive tasks—blood flow will increase to the visual cortex while you are watching a movie, for example—a device that shows blood concentration and oxygenation changes can help researchers and medical professionals monitor brain activity. This is known as functional imaging.

"In breast imaging you just want to see blood vessels because they can reveal the presence of a tumor [tumors secrete chemicals that stimulate blood vessel formation]" Wang says. "But the functional change in imaged brain activity is only a few percent change in the baseline signal. That's more than an order of magnitude harder to measure."

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