Monte Carlo Study Of Spatial-resolved Diffuse Reflectance At Short Source-detector Separation

The spatially resolved diffuse reflectance of biological tissues has been studied experimentally and theoretically for many years, and widely used for the determination of the optical properties of the tissues. Both the diffusion approximation theory and Monte Carlo simulation are usually used in the research, but the diffusion approximation theory fails to describe accurately the reflectance at a short source-detector separation. The diffuse reflectance close to the source is studied by Monte Carlo simulation in this dissertation. The influences of the optical parameters and the sources on the reflectance are studied, and the results are compared with that of the analytical model.Firstly, the different phase functions are discussed in detail, and the n-order parameters of the phase functions are introduced, especially the second-order parameter and third-order parameter are chiefly discussed. According to the relation of the second-order parameter and the first-order moment, the applicable region of each phase function is brought forward. Secondly, the development history and the function of the Monte Carlo method are introduced systemically, and then the processes of the light transport in the tissue are also described amply. Thirdly, the spatially resolved diffuse reflectance is studied at short source-detector separation with Monte Carlo simulation, the conclusion is that the properties of tissue properties can be approximately described by the absorption coefficient, the reduced scattering coefficient and the refractive index in the region farther than several transport mean free paths( mfp '), but a second-order parameterγis needed to describe the properties of the tissues in the region close to the source Finally, the Monte Carlo program is properly modified for different light sources. The infinitely narrow photon beam is replaced by the buried isotropic photon source, the effects of the different light sources on the diffuse reflectance are studied, and the validity of both the diffusion approximation theory and P₃ approximation theory are checked up.