Using Time-Reversal Ultrasound To Improve Medical Imaging and Therapy

Researchers at Washington University in St. Louis have combined ultrasound and visible light in a novel way that shows great promise in the quest to “see” deeper into the human body.
The advantage of light is, of course, that it is in the frequency range at which human eyes can visualize, but unfortunately, the degree to which the photons scatter prevents us from seeing very deep in tissue. Ultrasound, on the other hand, doesn’t suffer as much from the scattering problem, but primarily reveals only density and compressibility, which isn’t always that helpful.
Dr. Wang has combined two techniques of biomedical imaging to combine the best attributes of ultrasound and light. The first technique, ultrasound tagging of light, involves passing light through an ultrasound beam, which “tags” certain photons in the area of interest. The other technique, called time reversal, defies easy explanation, but involves sending waves backward along exactly the same path by which they arrived (please see links for a more detailed explanation).
Dr. Wang, professor of biomedical engineering at Washington University in St. Louis, says "Focusing light into a scattering medium such as tissue has been a dream for years and years, since the beginning of biomedical optics. We couldn’t focus beyond say a millimeter, the width of a hair, and now you can focus wherever you wish without any invasive measure."
This technique, coined time-reversed ultrasonically encoded (or TRUE), allows light to be focused in a controllable location within tissue. As you can imagine, this holds vast promise for imaging as well as "phototherapeutics" – we look forward to seeing this technology brought to market for research and clinical use and, as always, will keep you posted.
Press release: Guide star lets scientists see deep into human tissue…
Abstract in Nature Photonics: Time-reversed ultrasonically encoded optical focusing into scattering media