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Superficially scattered photons can be selected by obliquely illuminating a tissue with linearly polarized light and imaging the tissue site with a simple CCD camera through a second linear polarizer that is oriented either parallel to the illumination (PAR) or perpendicular to the illumination (PER). Both images are similar, with about 90% of the light being multiply scattered light that has lost its polarization orientation. The difference image, PAR - PER, substracts this common background of multiply scattered light and selects only photons that have been scattered in superficial tissue layers and retain the polarization orientation of the illumination light.
In this report, we used an RGB camera to acquire PAR and PER images and to calculate the PAR - PER for each of the red, green and blue channels. A new color image based on PAR - PER was created which revealed the colors of the tissue when viewed only with superficially scattered photons. We imaged an excised mouse esophagus. Some regions of the tissue appeared red and other regions appeared blue, putatively due to how the tissue ultrastructure (eg., collagen fiber bundles, nuclei, mitochondria, lipid membranes) interacted with different wavelengths of light. The wavelength dependence of scattered polarized light offers a mechanism of contrast for imaging and characterizing biological tissues.