Jacqmin D
University of Wisconsin-Madison, Madison, WI.
Med Phys. 2012 Jun;39(6Part3):3623. doi: 10.1118/1.4734709.
The purpose of this work is to demonstrate that optical photon Monte Carlo simulations via a photon transport code called MCML can be accelerated using macro Monte Carlo (MMC) techniques.
MCML was modified to incorporate the macro Monte Carlo radiation transport method. The original MCML uses scattering, absorption, reflection and refraction physics to transport optical photons through multi-layered geometries. The code determines transmission, reflection and absorption for the layered geometry specified by the user. To make the code run faster, the MMC version of MCML uses large, multi-interaction steps in regions that are homogeneous. These large steps are pre-computed and stored in a database with many step sizes, materials and photon energies. The MMC version of MCML determines whether large MMC steps or traditional Monte Carlo should be used depending on the photon's current location inthe geometry.
The MMC version of MCML was tested against the original MCML code for a number of simple test geometries. It was also tested in anatomical geometries that are often uses in optical photon modeling. This includes skin and skull geometries. In each case, the reflection and transmission results from each code differed by less than 0.5%. The absorption data produced by each code also differed by less than 0.5% in most cases, and never differed by more than 2%. The MMC version of MCML runs between 1-3 times as many particles per unit time comparedto MCML, depending on the geometry.
Applying Macro Monte Carlo methods to MCML produces a faster code without compromising accuracy. The speed-gains are greatest in geometries thathave regions that are large relative to the mean scattering length for photons in that region. This work has the potential to accelerate light modeling for both photodynamic therapy and near-infrared spectroscopic imaging.
本研究旨在证明，通过名为MCML的光子传输代码进行的光学光子蒙特卡罗模拟可以使用宏观蒙特卡罗（MMC）技术来加速。
对MCML进行修改，以纳入宏观蒙特卡罗辐射传输方法。原始的MCML使用散射、吸收、反射和折射物理原理，通过多层几何结构传输光学光子。该代码确定用户指定的分层几何结构的透射、反射和吸收。为了使代码运行得更快，MCML的MMC版本在均匀区域中使用大的多相互作用步长。这些大步长是预先计算并存储在一个包含许多步长、材料和光子能量的数据库中。MCML的MMC版本根据光子在几何结构中的当前位置，确定是使用大的MMC步长还是传统的蒙特卡罗方法。
针对一些简单的测试几何结构，对MCML的MMC版本与原始MCML代码进行了测试。还在光学光子建模中常用的解剖几何结构中进行了测试。这包括皮肤和颅骨几何结构。在每种情况下，每个代码的反射和透射结果相差不到0.5%。在大多数情况下，每个代码产生的吸收数据也相差不到0.5%，且差异从未超过2%。根据几何结构的不同，MCML的MMC版本每单位时间运行的粒子数是MCML的1至3倍。
将宏观蒙特卡罗方法应用于MCML可产生一个更快的代码，且不影响准确性。在相对于该区域光子平均散射长度较大的区域的几何结构中，速度提升最大。这项工作有可能加速光动力疗法和近红外光谱成像的光建模。
