Diffusion approximation based convolution method for spatial resolved reflectance of biological tissues irradiated by photon beams with finite diameter

摘要

In this paper, a mathematical expression of reflectance point-spread-function, that is defined as the spatial distribution of light diffuse-reflected from biological tissues irradiated by pencil light, is derived from the diffusion approximation (DA) theory. Through calculating partial derivative of the reflectance point-spread function with respect to effective scattering coefficient, we proposed a quantitative criterion for the applicability of diffuse approximation. Moreover, by the introduction of the reflectance point-spread-function, we can use convolution method to calculate the spatial resolved reflectance from dense and thick tissues irradiated by photon beams with finite diameter. We called this method DA based convolution method. Numerical calculations show that the DA based convolution method has much higher computing efficiency compared with the Monte Carlo method.