Will Photoacoustic Imaging Successfully Map the Brain?

The brain is an amazing organ. In the past fifty years we've made significant progress in understanding neurons and brain cell operation. Many areas of the brain continue to mystify, particularly the real-time cooperation between millions of brain cells, neurological diseases such as Alzheimer's and Parkinson's, and mental illnesses such as depression.

A little over two years ago, President Obama announced the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative, a research effort focusing on developing a dynamic understanding of brain function in hopes of making headway in treating brain disorders. Brain imaging-more or less a prerequisite for successful mapping-is too slow or low-res to map real-time brain function. But photoacoustic imaging, a technology pioneered by a few small research groups, might hold the key to unlocking full-brain imaging.

Light and sound are both widely used for medical imaging, but each has significant drawbacks. Light scatters after entering a sample, resulting in poor surface penetration beyond about a millimeter as well as blurry imaging. Ultrasonic wavelengths penetrate well and don't scatter as much, but lack resolution and clarity. Lihong Wang, a researcher and professor of biomedical engineering at Washington University in St. Louis, reasoned that combining both methods might eliminate the weaknesses of both; he's subsequently become a photoacoustic imaging pioneer.

Wang and his team have built several photoacoustic microscopes to date. These operate by delivering non-ionizing laser pulses into a skull. Some of this energy is converted to heat after entering the brain, and through transient thermoelectric expansion emits distinctive wideband ultrasonic radiation. An ultrasonic transducer detects this emission, analyzes it, and converts it into an image. Combining the two technologies results in high-res imaging with the penetrative abilities of ultrasound. (Wikipedia has a handy imaging comparison table.)

Photoacoustic imaging is also fast: this year Wang's lab constructed a high-resolution image of a mouse brain operating in real-time. He's also augmenting the technology by implementing ultra-high-speed cameras to capture light propagation. The team envisions the eventual development of a real-time medical tricorder a la Star Trek, in which a full-body scan would instantly reveal issues and conditions. (I wouldn't know anything about that, though...)

It seems safe to assume that we'll see widespread photoacoustic imaging in the near future, not only for brain scans but for other medical imaging as well. Wang's work is cool in that he applies existing technologies-his idea for targeting light at individual cells came from astronomy, for example-and puts them to novel uses in medicine. In addition to brain imaging, photoacoustic imaging is useful for investigating the formation of blood vessels in tumors, melanoma detection, and blood oxygenation mapping-not quite to the reach of Star Trek's final frontier, but getting there.

Image credits: University of Rochester Medical Center | Wikipedia