Yang Xue, Li Gang, Liu Yan, Zhao Jing, Lin Ling
Guang Pu Xue Yu Guang Pu Fen Xi. 2016 Nov;36(11):3476-80.
Typically, it is time-consuming to use Monte Carlo simulation to model light propagation in turbid media, such as breasts, mainly because of the thick simulated tissue and the large number of photons required by the stochastic nature of MC simulations. In this paper, in view of the light source and the receiver in a straight line, the transmitted light received by optical fiber model is analyzed; in terms of the optical properties of biological tissue itself, implementation of boundary constraint conditions and restriction of the number of backscatter events have been developed to reduce the simulation time. It is verified that the calculation is relatively simple by many experiments, when the position after two scattering is regarded as the demarcation and the boundary constraint conditions are efficiently solved by optical parameters of tissue respectively. At the same time, considering the actual situation in incident and emergent position, the boundary constraint conditions are expanded. The number of backscatter of every photon that received by optical fiber in the same position are recorded and tissues are selected different thickness and the similar optical parameters in the simulations. Additionally, it is found that the number of backscatter would increase as the depth of tissue or scattering coefficient increases, or as absorption coefficient or anisotropic factor decreases. Therefore, the time is saved further through limiting the number of backscatter. The simulation results show the combination of those new methods reduces the operation time of the MC simulation by 50% on a typical desktop computer. Those new methods are especially suitable for MC simulations of the thick tissue or the scatterer with a complex boundary. This acceleration method is applicable when light source and receiver are in a straight line the biological tissue is thicker and scattering coefficient is large. It can effectively save needed time and be beneficial to analyze the transmission imaging.
通常，使用蒙特卡罗模拟对诸如乳房等浑浊介质中的光传播进行建模非常耗时，主要是因为模拟组织较厚以及蒙特卡罗模拟的随机性质需要大量光子。本文针对光源与接收器在一条直线上的情况，对光纤模型接收到的透射光进行了分析；从生物组织本身的光学特性出发，通过实现边界约束条件和限制后向散射事件数量来减少模拟时间。经多次实验验证，当将二次散射后的位置作为分界点，并分别利用组织的光学参数有效求解边界约束条件时，计算相对简单。同时，考虑到入射和出射位置的实际情况，对边界约束条件进行了扩展。记录光纤在同一位置接收到的每个光子的后向散射次数，并在模拟中选择不同厚度但光学参数相似的组织。此外，发现后向散射次数会随着组织深度或散射系数的增加，或者随着吸收系数或各向异性因子的减小而增加。因此，通过限制后向散射次数进一步节省了时间。模拟结果表明，这些新方法的结合在典型台式计算机上可将蒙特卡罗模拟的运行时间减少50%。这些新方法特别适用于对厚组织或具有复杂边界的散射体进行蒙特卡罗模拟。当光源和接收器在一条直线上、生物组织较厚且散射系数较大时，这种加速方法适用。它可以有效节省所需时间，有利于分析透射成像。
