Measurement Of The Complex Refractive Index Of Tissue Based On The Derivative Total Reflection Method And Application Research

Refractive index(RI) is an important optical parameter of biotissue, which can be defined in terms of a real part nr and an imaginary part ni. n=nr+ini, where ni equals to the extinction coefficient κ, which means energy decay per unit at certain direction caused by absorption and scattering. In the area of diagnosis of disease and manufacture of optical information devices, the requirement for information of refractive index is growing for a lot of problems of precisely measurement require the RI information.When using diffusion-approximation-based inverse model to determine the tissue optical parameters, RI is used as a known parameter and therefore its measurement accuracy affect the precise determination of other optical parameters. When Monte-Carlo method is used to simulate the light propagation in biotissue, RI determines the photons directions and boundary mismatch. It has been proved theoretically and experimentally that measurement of optical properties can be substantially affected by RI. In this thesis, we use the Derivative total reflection method (DTRM) to study the following problem:(1) The theory and arithmetic of DTRM is detailed introduced and the method is used to determine the complex RI of biotissue.(2) We propose an extended derivative total reflection method (EDTRM), by which both of the refractive index and the extinction coefficient can be determined simultaneously. The method is used to determine the complex RI of biotissue and a series of tissue-mimicking phantoms commonly used in biomedical field.(3) For samples with multielement, a new modified model of DTRM is proposed. The modified model is verified through experimental results of simulation sample made of binary and ternary materials. The modified model is also used for the RI measurement of solid material with multielement.(4) We discover and investigate the effect of tissue fluid on the measurement of complex refractive index of animal tissue. We discover that the existence of the tissue fluid at the prism-sample interface is unavoidable in the measurement and has an important effect on the determination of RI of animal muscle tissue. The contacting area of tissue sample consists of the tissue fluid and muscle tissue. Coupled with polarized optical reflectance measurements performed on several kinds of animal muscle tissues, RIs of tissue liquid and biotissue were resolved using the modified model for material with multielement. The proportion of the tissue liquid was also calculated. For biotissue with multielements, the RIs and the proportions of main components are also calculated using the modified DTRM.(5) We provide a methodical and systematic experimentation of the dynamic refractive index (RI) change of tissue under stepped compression load using a custom-built pressure apparatus. Angle-dependent reflectance profiles of biotissue samples are recorded and the RI values are resolved using the modified DTRM. Clear and quantitative relationships between RI change as well as the reduction of tissue fluid and the applied pressure are given. The results can fill the void of related database for RI values of tissue under pressure. Results are useful for investigation of the mechanism of mechanical optical clearing, tissue dynamics under mechanical stimuli and other biomedical application.(6) The application of matching liquid on the measurement of the refractive index (RI) of biotissue using total internal reflection (TIR) method is investigated in detail. For tissue with different absorbing and scattering ability, adequate model was built. The theoretical calculation is verified by experimental results of three simulation samples. Reflectance curves of porcine tissue samples were recorded and systematically studied using two kinds of matching liquid. Experimental observations of biotissue (’Double Peaks’and’Triple Peaks’on derivative curves) are successfully explained by the theoretical model. At the end, rules for preparation of samples and selection of matching liquid for biotissue RI measurement are summarized.(7) We report that the RI of each component of the solid mixture can be extracted simultaneously using the modified DTRM without the necessity of smashing the sample into powder or using a strict matching liquid. The proportion of each component in the illuminated area can also be obtained by data fitting without additional measurement. Granite and Marble samples were measured, and the RI of each component was resolved. The RI differences of the specific area are useful indicators for identification of marble sample.(8) DTRM is used for study of the thickness of graphene, which is a new material. Graphene samples transferred on transparent substrate are measured. An easy procedure based on Fresnel formula is provided for easily extracting the layer information of graphene and the RI of the substrate. DTRM provides a means for rapidly determining of the layer information of graphene. The results show good agreement with the Raman spectra.