Research On The Scattering Properties Of Biological Tissue With Optical Coherence Tomography

The accuracy measurement of optical properties of biological tissues is one of the most basic problems in tissue optics and biomedical photonics. It has important theoretical value and practical significance on photodynamic treatment and diagnosis in medicine. Over the years, people have been exploring effective ways to measure the optical properties of biological tissues (such as refractive index, absorption coefficient, scattering coefficient and scattering anisotropy factor, etc.).However, the heterogeneity of biological tissues, mainly the inhomogeneity of the refractive index, makes the light unable to penetrate biological tissue, which creates difficulties in extracting a clear image and limits the rapid development in tomography imaging and optical parameter measurement techniques of tissues.This thesis carried out theoretical analysis and experimental study on the transmission of light in biological tissues and the measurement of the tissue optical properties by OCT.The main works of this thesis are as follows:1. The principle of OCT is analyzed, the resolution of OCT imaging is discussed. The center wavelength and bandwidth of light source directly affect the axial resolution. The lateral resolution depends on the numerical aperture of objective lens in the sample arm. The lateral resolution and detection depth should be compromised.2. An OCT experimental platform with dual reference arms is designed and built up. The different application of the two reference arms has been introduced in detail, and their advantages and disadvantages have been analyzed. The refractive indices of tissue phantoms and some biological tissues have been measured accurately by the bOCT experimental platform.3. The theory of extended Huygens-Fresnel (EHF) model has been introduced. The effect of the changes of scattering coefficientμs the anisotropy factor g on the heterodyne effect factor, and the difference between the single scattering and the multiple scattering has been analyzed. Under the condition of specular reflection, the scattering properties of tissue phantoms are extracted by the use of the EHF model. The experiments show that the results of EHF model are similar to Monte Carlo simulation results which proved that EHF simulation model of experimental system is practical and is able to correctly extract the tissue optical properties.The work, which has been done in this thesis about the measurements of the scattering coefficients of biological tissues, has some new ideas and practical value, and can provide some reference to the measurement of tissue optical properties by OCT.