Improved imaging through human tissue using compensated transillumination

Summary form only given. A simple and robust approach to improving image uniformity for transillumination is to surround the imaged tissue with a medium of matching scattering and absorption properties. In this manner, a uniform transillumination image is obtained and the maximum dynamic range is available to examine variations a thin the tissue. When the match between the tissue and immersion medium is good, the human tissue will almost disappear, and the image will only show contrast due to small variations within the tissue. Thus the image shows contrast due to internal variations, which is what one wants, rather than due to tissue contours. A mixture of Ropaque and methylene blue dye are used as a matching immersion medium. Ropaque consists of a suspension of hollow polymer spheres in water. A frequency domain technique is used to measure the absorption and scattering properties of a human hand in vivo and to match the properties of the medium to the hand. With this method, one can independently determine the amount mismatch in absorption and scatter coefficients between the medium and tissue. When the match is good, there is very little difference in optical transmission between tissue and the matching medium; the authors found an RF amplitude decrease of 4% and a phase variation of -0.4 degrees when a fingertip was inserted between the optical fiber bundles in the matching medium. Details of determining the match are reported elsewhere.