Study Of Light Transmission In Biological Tissues By Monte Carlo Method

Energy distribution in biological tissue has a very important significance in laser biomedical information on the diagnosis and treatment. Monte Carlo method has been widely used in particle transport problem, but also fit in the light transport problem. Numerical results obtained by Monte Carlo method have become a non-test standards to compare the accuracy of various analytical theory of tissue optics.The basic idea of Monte Carlo method used in biological tissue optical energy transmission and distribution is:using the principle of absorption and scattering of photons to track the photons propagate through the medium of chaos; through the statistics simulation results of a large number of photon to obtain the distribution of laser energy within the bio-tissue.Firstly, the paper introduces the study history and the current situation of light energy distribution, provides an overview of the development of optical tissue and research mission; points out the research significance of light energy transferring in biological tissue.Secondly, introduce the structural characteristics and optical properties of biological tissue, sum up the interaction ways of the light with biological tissue, and focus on discusses the physical meanings of the optical parameters. Base on this, introduce the transmission model and the diffusion equation from diffusion approximation.Then, introduce the basic idea of Monte Carlo method and illustrate the use of it on energy distribution in biological tissues. According to the previous introduction of biological tissue structure characteristics and theoretical foundation, respectively give the optical model and simulation process of single-layer,double-layer and multi-layer biological tissues. Photon's launching, absorption, scattering, the probability sampling of direction and step-size, the relevant formula of absorption and scattering, colliding with boundary and the termination of photons are introduced respectively. The differences of photons propagation in multi-layer and single-layer bio-tissues are discussed in detail.Finally, the Monte Carlo simulation results of energy distribution in single-layer and multi-layer tissues are analyzed. Firstly the track of photons propagation is presented on two-dimensional view. Discuss the relationship between g factor, absorption coefficient, scattering coefficient and energy distribution on tissue surface. On this basis, analyze the transportion of light in single-layer and multi-layer tissues respectively.The light intensity distribution with depths in single-layer tissue by a collimated light beam and the influence of optical parameters in energy aggradations are presented. As to multi-layer tissues, the absorption energy density and internal fluence with depths and radius, the change of radially and angularly resolved diffuse reflectances are discussed separately. The transportion of the Gaussian beam and circularly flat beam in bio-tissues is simulated by the use of convolution.The obtained results have practical significance.