Astronomers have a neat trick they sometimes use to compensate for the turbulence of the atmosphere that blurs images made by ground-based telescopes. They create an artificial star called a guide star and use its twinkling to compensate for the atmospheric turbulence.
Lihong Wang, PhD, the Gene K. Beare Distinguished Professor of Biomedical Engineering at Washington University in St. Louis, has invented a guide star for biomedical rather than celestial imaging, a breakthrough that promises game-changing improvements in biomedical imaging and light therapy.
Wang's guide star is an ultrasound beam that "tags" light that passes through it. When it emerges from the tissue, the tagged light, together with a reference beam, creates a hologram.
When a "reading beam" is then shown back through the hologram, it acts as a time-reversal mirror, creating light waves that follow their own paths backward through the tissue, coming to a focus at their virtual source, the spot where the ultrasound is focused.
The technique, called time-reversed ultrasonically encoded (TRUE) optical focusing, thus allows the scientist to focus light to a controllable position within tissue.
Wang thinks TRUE will lead to more effective light imaging, sensing, manipulation and therapy, all of which could be a boon medical research, diagnostics, and therapeutics.
In photothermal therapy, for example, scientists have had trouble delivering enough photons to a tumor to heat and kill the cells. So they either have to treat the tumor for a long time or use very strong light to get enough photons to the site, Wang says. But TRUE will allow them to focus light right on the tumor, ideally without losing a single tagged photon to scattering.
"Focusing light into a scattering medium such as tissue has been a dream for years and years, since the beginning of biomedical optics," Wang says. "We couldn't focus beyond say a millimeter, the wid
|Contact: Diana Lutz|
Washington University in St. Louis