Diffuse photon transport in tissue-like media: Resolution limit for near-infrared imaging and an instrument for clinical spectroscopy of tissues

In this work I present the model for diffusive photon transport in tissue-like media along with solutions for a point source in infinite and semi-infinite media. Based on these solutions and experimental measurements, I consider the ultimate resolution of near-infrared based imaging of tissues using a simple model to describe resolution. I conclude that for a 5 cm thick tissue, the closest two objects buried in the center can be, and still be resolved is roughly 1.5 centimeters. I also show that light applied to the surface of a tissue-like medium, and detected on the same surface some distance away, penetrates into the medium. The depth of penetration is on the order of centimeters depending on the transport properties of the medium and source-detector separation. Since this light penetrates into tissue, and there is a model which describes how the transport of light through tissues depends on the tissue optical properties with sufficient accuracy, noninvasive tissue spectroscopy in the near-infrared is possible. During my thesis work a functioning tissue spectrometer was developed to demonstrate this point. I conclude by discussing measurements I made with this spectrometer on both laboratory samples and live patients. My experiments with the tissue spectrometer were instrumental in both demonstrating its capabilities and understanding advances to be made in the next generation of the device.U of I Onlythesi