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20 April 2005 Experimental test of depth dependence of solutions for time-resolved diffusion equation
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The determination of optical properties of a semi-infinite medium such as biological tissue has been widely investigated by many authors. Reflectance formulas can be derived from the diffusion equation for different boundary conditions at the medium-air interface. This quantity can be measured at the medium surface. For realistic objects, such as a mouse, tissue optical properties can only be determined at the object surface. However, near the surface, the diffusion approximation is weak and boundary models have to be considered. In order to investigate the validity of the time resolved reflectance approach at the object boundary, we have estimated optical properties of a liquid semi-infinite medium by this method for different boundary conditions and different positions of the fibers beneath the surface.The time-correlated single photon counting (TCSPC) technique is used to measure the reflectance curve. Our liquid phantoms are made of water, white paint and Ink. Laser light is delivered by a pulsed laser diode. Measurements are then fitted to theoretical solutions expressed as a function of source and detector’s depths and distance.By taking as reference the optical properties obtained from the infinite model for fibers deeply immersed, the influence of the different boundary conditions and bias induced are established for different fibers' depths and a variety of solutions. This influence is analyzed by comparing evolution of the reflectance models, as well as estimations of absorption and reduced scattering coefficients.
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Aurelie Laidevant, Anabela da Silva, Michel Berger, and Jean-Marc Dinten "Experimental test of depth dependence of solutions for time-resolved diffusion equation", Proc. SPIE 5745, Medical Imaging 2005: Physics of Medical Imaging, (20 April 2005);

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