Photoacoustic Imaging Optimizes Visualization of Cancerous Tissues Using Time Reversal Technology

Current high-resolution optical imaging technology allows researchers to see about 1-mm-deep into the body. In an effort to enhance this imaging technology, the investigators are employing photoacoustic imaging, which combines light with acoustic waves (sound), to form a clearer image, even several centimeters into the skin.

Washington University in St. Louis (MO, USA) engineers are using the photoacoustic approach to monitor the movement inside the body’s tissues to improve imaging of cancerous tissues and to develop potential treatments. Lihong Wang, PhD, a professor of biomedical engineering at the School of Engineering & Applied Science, is the lead investigator.

Beyond 1 mm into the body, the light scatters and obscures the features, which is why one cannot see bones or tissue in the hand with a flashlight. To overcome this, the engineers used photoacoustic imaging, and published their findings online November 2, 2014, in the journal Nature Photonics. The new technology, called time-reversed adapted-perturbation (TRAP) optical focusing, sends guiding light into tissue to seek movement. The light that has traversed stationary tissue appears differently than light that has moved through something moving, such as blood. By taking two consecutive images, they can subtract the light through stationary tissue, keeping only the scattered light due to motion. Then, they send that light back to its original source via a process called time-reversal so that it becomes focused once back in the tissue.

“This can potentially be used in imaging or therapy,” Dr. Wang said. “For example, focusing pulsed light on port wine stains, which are excessive growth of blood vessels, could remove the stains without damaging the surrounding normal skin.”

In 2011, Dr. Wang’s lab was the first to use ultrasound focusing to provide a virtual, noninvasive internal guide star that allowed them to focus on anything moving in tissue. But TRAP focusing is much more effective in tracking moving targets, according to Dr. Wang. TRAP focusing can enhance and contrast by redistributing and concentrating light on the targets, allowing for images to be captured from greater depths.

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