Diffuse Reflection Associated With Scattering Phase Function From A Micro-region Close To The Source

The determination of the optical parameters of biological tissue and optical parametric measurement technology has received a great deal of attention,because these optical parameters can be further used to obtain morphological, biochemical and histochemical information. Absorption coefficient ?a, scattering coefficient ?s and anisotropy factors g have been obtained by a variety of measurement techniques,however, due to different measurement methods, these parameters are very different.For example, due to diffusion approximation theory only applicable to the case away from the light source, so there is a big model error close to source, resulting in reduced accuracy of the optical parameters of the inversion. However, in many cases you need to measure diffuse reflectance near the micro-region close to the source, for example, using an endoscopic approach to detect in vivo or measurement of small volume of biological tissue. The problem of diffuse reflection near the micro-region close to the source is more complex than the diffusion approximation model, which is due to biological tissue scattering phase function (SPF) have a greater impact on the diffuse light distribution. Influence of the SPF on the diffuse reflection of a micro-region close to the source is investigated by Monte Carlo (MC) simulations.The main work includes the following:1. By studying several common SPF, the research shows the trend of the second order parameter with anisotropy factor and the trend of third-order parameter ? with ?are the same for three combinations phase function, therefore, Influence of one of three combined phase function on the diffuse reflection of a micro-region close to the source is investigated. When the scattering properties of the actual tissue needs to use combined phase function to describe, If Henyey-Greenstein phase function is used to fit the experimental data, it will lead to large errors in the determination of optical parameters.2. Based on the diffusion approximation of radiative transfer equation?MC numerical model and based on the semi-empirical analytical model of the photon migration theory, and suitable for small aperture semi-empirical analytical model with high order parameters is derived on the basis of the semi-empirical analytical model.The model is mathematically simple, not limited diffusion approximation and suitable for the measurement of sources close to the radiation field.3. The variation of diffuse reflectance with ? is studied and a semi-empirical expression containing ? is derived. The research shows that when using a set of parameters (g,?) represents SPF, the SPF difference in the reaction of the third-order parameter ? ; diffuse reflectance decreases with the increase in ? , and influence of ?on the diffuse reflectance can reach 9%.4. The relationship between a semi-empirical model of diffuse reflection and the optical parameters related to the phase function is analyzed. Research shows that the scattered light of the micro-region close to the source is very sensitive to the SPF,and the sensitivity will gradually weaken with increasing of collection aperture ?.When ?> 1.8mm influence of the SPF on the diffuse reflection is not obvious and relative change in reflectivity is less than 1%; when ?<1.8mm, influence of the SPF on the diffuse reflection can reach up to 15.2%.