Model For The Biological Tissue Reflectance Measurement With Small Aperture And Experimental Research

Due to the strong scattering properties of biological tissue in near-infrared spectral region, the near-infrared light can only reach a certain depth within the tissue, with a portion of the light absorbed, and the rest scattered back to the tissue surface, namely diffuse reflectance. Diffuse photon carries important messages of biological tissue,therefore diffuse reflectance measurement has great potential in non-invasive or minimally invasive optical detection technique. Measurement techniques based on spatially resolved diffuse reflectance have been widely used in the biomedical field,which requires distance between light source and detector be greater than several transport mean free path, and it usually takes more than a few millimeters. This requirement limits the application of these techniques. For example, endoscopic approach based detection in vivo requires measurement of the diffuse reflectance near the micro-region of the light source. However, the lack of exact analytical solution limits its applications.This paper studies the measurement model for diffuse reflectance near the micro-region of the light source with small aperture, and the main research and innovation include:1.Based on the diffusion approximation and1?-P approximation, analytical models of diffuse reflectance measurement with small aperture are derived. The feasibility of diffuse reflectance measurement with these models near the micro-region of the light source has also been analyzed.2.A semi-empirical formula of diffuse reflectance measured via small apertures is elaborated on the basis of Monte Carlo method. And a function relation between the reflectivity and the aperture, relative refractive index is firstly determined. Based on this semi-empirical formula, the inversion of optical parameters in turbid biological media is done and its application range is analyzed.3.Based on above research, under the weak absorption condition, a linear semi-empirical model is established, the effect of anisotropic factor on the model is studied, optical parameters are recovered from the data using Monte Carlo simulation,The validity of the model is verified by analyzing the relative error between the inversion results and the true values.4.Experimental methods of the biological tissue reflectance measurement withsmall aperture are studied. Several measuring devices for diffuse reflectance,including multi-diameter single fiber device, a single optical fiber scanning device and an optical fiber array measuring device have been elaborated. We compare the data acquired by single optical fiber scanning and optical fiber array measuring with those by Monte Carlo simulation. These data have also been converted to suit various apertures and compared with the semi-empirical analytical solutions obtained by the methods proposed in this dissertation, which is suitable for small aperture measurement.