Instrumental Analysis

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Abstract

Two main topics constituted the main thrust of the optical imaging project. Because photons suffer significant scattering by cell components it is necessary to determine physical properties of photon trajectories in terms of some form of diffusion, random walk, or transport theory. Up till about the year 2000 the standard assumption was that optical tissue parameters were isotropic with respect to cell geometry. Since that time it has become more and more evident that this assumption is violated in a significant number of measurements. For example, photons tend to move preferentially along fibers. This phenomenon has stimulated our research on the effects of optical parameter anisotropy on techniques used to detect differences between normal and abnormal tissues as well as to estimate the amount of tissue interrogated by photons involved in optical measurements. A mathematical formalism, based on random walk theory, originally developed by members of MSCL to incorporate optical anisotropy has been used to produce a simple measure of the degree to which contrast due to the presence of an abnormal inclusion in a tissue is affected by the presence of optical anisotropy. A further project along these lines is that of determining how anisotropic optical parameters affects the amount of penetration of photons into a tissue as a measure of how much of the tissue is investigated in different types of imaging experiments. [unreadable] A presently popular technique in optical imaging related to cancer diagnostics and related animal models is based on fluorophore-conjugated probes. We have recently developed a model based on the continuous-time lattice random walk which considerably extends previous theoretical work on fluorescence lifetime imaging by removing rather severe restrictions imposed on the basic theoretical formalism previously described in the literature. Prior theory appears to be valid for fluorophore parameters that differ by two orders of magnitude from those measured in NICHD experiments. The theory developed by members of MSCL take this difference into account, as well as the absorption coefficient with results that differ significantly from the earlier published work on this subject. Work is continuing both on the theoretical development and on numerical techniques for estimating parameters necessary to translate experimental data into useable information. [unreadable] More recently we have begun an investigation of the effects of anisotropic optical coefficients on transillumination measurements in collaboration with members of NICHD. The basic results have been established and are presently being checked and extended.