Recently there has been considerable interest in the use of multiple scattered light in optical tomography, due in part to its potential applications in medicine. Spatial variations in the absorption and scattering properties of a given tissue reveal much about its metabolic state, vascularization, and structure. In addition, mapping the distribution of fluorescently tagged antibodies may provide a means of localizing subclinical tumors with great specificity. Our current studies have focused upon experimental validation of our numerical and analytical solutions of these integral equations. To date, we have successfully reconstructed images of phantoms whose absorption and scattering properties differ from background in a manner that approximates in situ, tumorigenic tissues. We have also incorporated fluorescently labeled probes into our phantoms and successfully reconstructed not only the object-s spatially dependent absorption and scattering properties, but also the spatial distribution of its fluorophores. More recently, we have conducted a series of sensitivity experiments aimed at determining the minimal fluorophore number densities needed for image reconstruction in inhomogeneously absorbing and scattering backgrounds. Preliminary findings suggest that, with additional sources and detectors, this technique may be of clinical value in the screening of subclinical breast carcinoma. In addition, we have begun to acquire photon diffusion images in vivo. At present the apparatus used in these studies operates in the time domain and is comprised of 24 sources and 8 detectors. The multichannel capability allows for the reasonably short acquisition times necessary for in vivo imaging. Two near-IR wavelengths that correspond to significant absorption coefficients in the hemoglobin and myoglobin spectra are used. Images of the human forearm are expected to reveal the spatial distributions of hemoglobin and myoglobin oxygenation during rest and finger flexion exercise. This work will have significant implications for muscle metabolism studies, since the relationship between oxygen supply and utilization within a muscle can be resolved spatially.
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