| It is important for biomedical photonics and medical diagnosis and therapy to investigate the propagation of light in biological tissue and optical properties of tissue, therefore, the light propagation in tissue and the measurements of optical properties of bio-tissues are studied in this thesis. Based on the light transport theory, the diffusion equation for light propagation in tissue was obtained. The diffusion equation was solved with different boundary conditions for semi-infinite geometry, when a narrow collimated light was normally incident upon the surface of a tissue, and the expressions of time-resolved and spatially resolved reflectance were also given. Two kinds of the experimental sets were designed to study the distributions of scattering light in the semi-infinite biological tissue phantoms and the influence of the boundary of tissue phantoms on the distributions of scattering light in tissue phantoms, and new experimental results of the characteristics of the distance-dependent intensity of scattering light in different directions and the influence of the boundary of tissue phantoms on the distributions of scattering light in tissue phantoms were obtained. The theoretical analyses for the experimental results were made by the diffusion theory and a new method for analyzing the experimental results was presented; the study of the influence of the boundary of tissue phantoms on the distribution of scattering light shows that the distribution of scattering light is mainly determined by the scattering of light in the tissue, and the influence of the reflection and transmission of light on the boundary of tissue phantoms on the form of distribution curves of scattering light is small, the improper expressions in some theses for this problem are clarified by our study. The simulations of the distributions of the fluence rate in a semi-infinite tissue by Monte Carlo method were made to test the accuracy of the diffusion theory with the three different boundary conditions. It is shown that the partial current boundary condition (PCBC) and extrapolated boundary condition (EBC) have good accuracy, and the expressions of diffusion theory with EBC are simpler than PCBE. The total time-resolved reflectance from a semi-infinite tissue was investigated, which based on the diffusion approximation with zero boundary conduction (ZBC) and extrapolated boundary conduction (EBC), and the total time-resolved reflectance with the ZBC solution and with the EBC solution were compared with that from Monte Carlo simulations. The corresponding diffusion equations were fitted to Monte Carlo simulations data to determine optical parameters. The effects of different boundary conditions on the accuracy of the deducing optical parameters were analyzed. The experimental sets were designed to measure spatially resolved reflectance and transmittance of surface of tissues by using optical fiber detector and CCD, and the analytic system of CCD image was developed by using C Language; the experimental results by use of CCD were compared with that of Monte Carlo simulations, it is shown that the CCD experimental setup and the analytic system of CCD image can be used for the study of the measurement of the spatially resolved reflectance and transmittance of biological tissues, and we have improved the method for the measurements of optical parameters by using CCD. The absorption and reduced scattering coefficients of bovine tissues are derived by nonlinear regressions of the solution of the diffusion equation for spatially resolved reflectance to relative reflectance data, and the differences between the results and the published data are less than 9.4%. The methods for determining absorption and reduced scattering coefficients of tissue by diffusion equation fitting experimental data or Monte Carlo simulations data were investigated. The experimental setup of optical coherence tomography was used for the image of the simulacrum of biological tissue, and the images of 100×50 pixels were obtained. The OCT experimental setup has the resolution of 20 μm transversely and 26 μm in axis direction, An OCT image of 100×100 pixels(2mm×2mm)can be captured within 3 minutes. We studied the relationship between the detected signal and the voltage or frequency, which was fed to the piezoelectric ceramic, and determined the appropriate values of the voltage or frequency fed to the piezoelectric ceramic; "The focus tracking method" and the "optical path shifting method", which are two kinds of methods for measuring the thickness and refractive index of bio-tissue, were presented. The refractive index of subsurface of a fresh cucumber was measured by using 1300nm and 850nm light sources. The results were 1.351±0.005 and 1.364±0.005 for 1300nm and 850nm respectively.
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