Reversing Time To Visualize Tumors
By Chuck Seegert, Ph.D.
New photoacoustic methods have enabled researchers at Washington University of St. Louis (WUSL) to visualize tumor structures non-invasively. Using visible light, the team expects to improve the ablation of cancer blood vessels and possibly other treatments.
Shining a flashlight through your hand leads to interesting colors passing through, but one wouldn’t expect to see details of blood flowing through the veins. Generally, the passage of light through opaque materials leads to scattering of that light and allows little or no resolution. Historically, a technique called photoacoustic imaging has been used to overcome this challenge. The method uses implanted or virtual “guide stars” to help with the scattering and develop images of tissues. But, the use of these guide stars may no longer be necessary, according to a recent press release from WUSL.
The technology is essentially a subtraction method that identifies objects in motion. Time-reversed adapted-perturbation optical focusing (TRAP) uses light to sense movement in the tissue. Tissue that isn’t moving, like muscle and bone, transmits light differently than those that contain items in motion like blood. Two images are taken, and light from the stationary tissues is subtracted from light passing through the objects in motion. Once it is determined where it came from, the light is sent back to its original source, which yields a focused image.
“This can potentially be used in imaging or therapy,” Lihong Wang, the Gene K. Beare Distinguished Professor of Biomedical Engineering at the School of Engineering and Applied Science at WUSL, said in the press release. “For example, focusing pulsed light on port wine stains, which are [dark birth mark-like areas on the skin that are caused by] excessive growth of blood vessels, could remove the stains without damaging the surrounding normal skin.”
While the use of a guide star has been effective in the past, the new TRAP method is much more effective, according to the press release. This is especially true with tracking objects in motion, since concentrating the light on these targets can provide images at greater depths than the guide star method.
Potential applications of the new technology include photoablation of angiogenic vessels, the blood vessels that promote tumor growth, according to a recent study published by the team in Nature Photonics. Additionally, imaging tumors to understand their extent may also be possible.
Photoacoustics is an area of diagnostic imaging that is gaining momentum in dermatology. Recent developments have allowed it to be used to understand the depth and extent of melanoma non-invasively.