6 February 2007 Reduced scattering coefficient determination by non-contact oblique angle illumination: methodological considerations
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Abstract
The reduced scattering coefficient, &mgr;s, was determined using oblique angle illumination and imaging backscattered light intensity. The distance &Dgr;r between the point of light incidence (hot-spot) and the circular symmetric diffuse reflectance centre, is ∼1/&mgr;s'. Previously, &Dgr;r was obtained analyzing a 1D strip aligned with the laser beam. We improved this method by calculating a 2D intensity image with extended dynamic range by assessing camera linearity, superimposing images with multiple integration times, and compensating for lens vignetting. The hot-spot algorithm utilises several images to minimize speckle variations and account for laser beam shape. Diffuse centre position is obtained by filtering the superimposed image with decreasing thresholds using momentum analysis to determine circular symmetry. The method was evaluated on 18 optical liquid phantoms with &mgr;s&egr;[1.5, 3.0] mm-1 and &mgr;s&egr;[0.01, 0.16] mm-1. The 2D method had better linearity with &mgr;s and smaller variations due to more stable hot-spot detection, than the 1D method. The anisotropy factor g was obtained by fitting measured and Monte Carlo simulated spatially resolved intensity decays and verified with a laser Doppler flowmetry technique. With an optimal compensation for the &mgr;a dependence, the rms error in &mgr;s' estimation was 2.9%.
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Tobias Lindbergh, Marcus Larsson, Ingemar Fredriksson, Tomas Strömberg, "Reduced scattering coefficient determination by non-contact oblique angle illumination: methodological considerations", Proc. SPIE 6435, Optical Interactions with Tissue and Cells XVIII, 64350I (6 February 2007); doi: 10.1117/12.698903; https://doi.org/10.1117/12.698903
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