| Abstract | Diffuse reflectance was applied to the biomedical studies (muscles, cardiac tissues etc.) in a form of either a direct pseudo-optical spectrum or its second derivative. The first derivative adopts advantages of both direct spectrum (high signal-to-noise ratio) and its second derivative (simplifying the consideration of light scattering contribution, S). In contrast to spectrophotometry of solutions, diffuse reflectance application to the analysis of turbid medium chromophores leads to non-trivial problems of contribution of light scattering, the choice of reference, and light pathlength. Under certain conditions, the first approximation of the Taylor series of S results in the known linear dependence of S on wavelength in the 650-1050 nm wavelength range. Then the light scattering contribution to the first derivative becomes a wavelength-independent offset. In contrast to the second derivative, the information on light scattering inside the tissue is not lost. Effect of reference on the measured spectra becomes negligible. Application of the first derivative allowed (i) determination of NIR light pathlength in muscle tissue, and (ii) quantification of hemoglobin myoglobin absolute concentration (in mM) in cardiac tissue during open-heart surgery. The first derivative approach may in general be applied to any chromophores in turbid (biological) media. |
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