Reflectance Spectroscopy in Tissue
Reflectance spectroscopy reports the absorption and scattering properties of tissue. Various strategies for separating the contributions of absorption and scattering in attenuation measurements have been proposed and evaluated. We have adopted broad band steady state methods that are based on either diffusion or P3 approximations to radiative transfer. Because of our interest in cancer and in photodynamic therapy in particular, we have been especially interested in monitoring hemoglobin oxygen saturation using reflectance techniques.
We have published on experimental methods for measuring spatially resolved diffuse reflectance spectra and on characterizing laboratory model systems that mimic optical properties of tissue. In M.G. Nichols et al. (1997) we described our first experimental results in model systems, which were based on a diffusion theory approximation method (see Group Publications). These ideas were extended to realistic tissue phantoms using intact human red blood cells in E.L. Hull et al. (Phys. Med. Biol., 1998), to phantoms containing red blood cells and mitochondria in Hull and Foster, Appl. Spectrosc. (2001), and to a rodent tumor model in vivo, where the effects of carbogen breathing on hemoglobin oxygen saturation were studied (E.L. Hull et al., Brit. J. Cancer 1999). An evaluation of near infrared reflectance spectroscopy in terms of a cryospectroscopy technique was reported in D.L. Conover et al. (2000). During his PhD thesis research, Ed Hull developed a method based on a higher order, P3, approximation to radiative transfer that recovers accurate absorption and scattering spectra in more highly absorbing media and at shorter source-detector separations (Hull and Foster, JOSA A 2001). The use of short source detector separations in the visible region of the spectrum is being developed further in the thesis research of Jarod Finlay.
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