| In the past few years there has been much interest in photon migration in tissue. As the optical scattering and absorption coefficients of biological tissue are related to the tissue morphology and biochemistry, and an understanding of the propagation of light in biological tissue is essential for the use of light for medical diagnosis and therapy, so the light transport in tissue and measurement of optical properties of biological tissues were studied all-round in this dissertation. Based on the light transport theory, the diffusion equation for light transport 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. The case of plane-wave collimated onto the tissue surface was also considered. Light propagation in two-layered turbid media having an infinitely thick second layer was investigated in the steady state and frequency domains. To test the accuracy of the diffusion theory, we simulated the distribution of light in the tissue by Monte Carlo method. Analytical expressions from diffusion theory are compared with Monte Carlo simulations. The effects of the choice of the boundary conditions and diffusion coefficients on the accuracy of the optical parameters are quantified, and criteria for accurate curve-fitting algorithms are developed. It is shown that the error in deriving the optical coefficients is considerably smaller for the solution, which uses the extrapolated boundary condition (EBC) and the diffusion coefficient independent of absorption coefficient than the other three solutions. Monte Carlo simulation also confirmed the results obtained from the diffusion equation for two-layered turbid media. A new experimental method has been developed to determine the scattering and absorption characteristics of a turbid material non-invasively, From the measurement of Intralipid-10%, it is demonstrated that the accuracy of the absorption and reduced scattering coefficients determined by our set were ?μ a μa=2.8%, ?μ s′ μs′=5.2% respectively. The tissues of ox, pig, and chicken were measured by the experimental set and the absorbing and reduced scattering coefficients were acquired respectively. An optical coherent tomography system was established. The system has the resolution of 20 μ mtransversely and 26 μ min axis direction. An OCT image of 100×100 pixels(2mm×2mm)can be captured within 3 minutes. We studied the relation between the detected signal and the voltage or frequency, which was inputted to the piezoelectric ceramic. The results showed that the detected signal changed resembling periodical with the voltage and the detected signal was maximum when the voltage was 7.5V. To reduce the heat effect of piezoelectric ceramic to the optic fiber, we selected the frequency far away from the resonance frequency of the piezoelectric ceramic. The measured resonance frequency was 20kHz , so we selected 6kHz as the input frequency of piezoelectric ceramic. Two kinds of methods for measuring the thickness and refractive index of bio-tissue simultaneously are presented, i.e, the "the focus tracking method" and the "optical path shifting method". The refractive index of subsurface of a fresh cucumber was measured by using 1300nm and 850nm light source. The results were 1.351±0.005 and 1.364±0.005 for 1300nm and 850nm respectively. From theoretical analysis, we showed that optical properties of tissue can be determined from backscattered power curves measured by a OCT. Our approach was based on a first-order scattering theory that relates the backscattered power to the total and backscattering coefficients of a tissue.
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