New imaging technique gets under the skin...deep
Using a combination of simple optical techniques, plain old white light, and image processing, two Lawrence Livermore researchers and a colleague from the City College of New York (CCNY) have developed a technique for imaging tissue structures--tendons, veins, tumors--deep beneath the skin. The ultimate goal of this research is to dramatically improve the ability to perform minimally invasive cancer detection. ''With a technique called spectral polarization difference imaging [SPDI], we use different wavelengths of light to reach different depths. We also use the polarization properties of the light to help us select the light that penetrates into the tissue and is reflected back out of the tissue as opposed to the light that bounces off the tissue surface,'' says Livermore physicist Harry Radousky, acting Director of University Relations. ''We then image the tissue structures at the different depths, based on how these structures absorb, scatter, and depolarize light. This technique, combined with fiber optics, charge-coupled-device cameras, and image enhancement calculations, allows us to image up to 1.5 centimeters inside tissue, far deeper than the millimeter depths managed by other existing optical techniques.'' The basic research to develop this technique was funded by the Department of Energy through one of its centers of excellence in laser medicine--the DOE Center for Laser Imaging and Cancer Diagnostics directed by Robert Alfano, M.D., at CCNY. A branch of this center is hosted at the Laboratory within the Materials Research Institute. wavelengths in the visible spectrum are scattered and absorbed within the tissue. For even longer wavelengths--those in the near-infrared spectral region--scattering and absorption of the photons is even further reduced.'' The light that passes through the filter then passes through a polarizer. The light that finally hits the tissue sample is thus not only of a given wavelength but also of a selected polarization. As photons penetrate the tissue, they interact with various tissue structures that may have optical properties different from those of the host tissue. Finally, some of the injected photons emerge from the tissue in the backscattering direction. The intensity of the backscattered light depends on the optical characteristics of the tissue at the sample's surface as well as below its surface at a particular location. Light that reflects from the surface (known as a spectral reflection) is polarized and can be removed with a second polarizer set to reject this light. This phenomenon is similar to the way sunglasses work to remove the polarized glare from surfaces, such as the water surface in a swimming pool. The light that backscatters from somewhere below the surface of the tissue is depolarized and consequently can pass through this second polarizer. This remaining light passes through a 50-millimeter camera lens, which is coupled to a CCD detector that captures the image in an exposure of a few milliseconds.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15007281
- Report Number(s):
- UCRL-ID-142278; TRN: US200415%%65
- Journal Information:
- Article from Science& Technology Review November 2000, Other Information: Article from Science& Technology Review November 2000; PBD: 1 Nov 2000
- Country of Publication:
- United States
- Language:
- English
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