Slade Adam Broadbent, Aguilar Guillermo
Bourns Hall A342, University of California, Riverside, Riverside, CA 92521, USA.
Bourns Hall A345, University of California, Riverside, Riverside, CA 92521, USA.
Comput Methods Programs Biomed. 2015 Feb;118(2):234-41. doi: 10.1016/j.cmpb.2014.11.007. Epub 2014 Nov 27.
The Monte Carlo method for photon transport is often used to predict the volumetric heating that an optical source will induce inside a tissue or material. This method relies on constant (with respect to temperature) optical properties, specifically the coefficients of scattering and absorption. In reality, optical coefficients are typically temperature-dependent, leading to error in simulation results. The purpose of this study is to develop a method that can incorporate variable properties and accurately simulate systems where the temperature will greatly vary, such as in the case of laser-thawing of frozen tissues. A numerical simulation was developed that utilizes the Monte Carlo method for photon transport to simulate the thermal response of a system that allows temperature-dependent optical and thermal properties. This was done by combining traditional Monte Carlo photon transport with a heat transfer simulation to provide a feedback loop that selects local properties based on current temperatures, for each moment in time. Additionally, photon steps are segmented to accurately obtain path lengths within a homogenous (but not isothermal) material. Validation of the simulation was done using comparisons to established Monte Carlo simulations using constant properties, and a comparison to the Beer-Lambert law for temperature-variable properties. The simulation is able to accurately predict the thermal response of a system whose properties can vary with temperature. The difference in results between variable-property and constant property methods for the representative system of laser-heated silicon can become larger than 100K. This simulation will return more accurate results of optical irradiation absorption in a material which undergoes a large change in temperature. This increased accuracy in simulated results leads to better thermal predictions in living tissues and can provide enhanced planning and improved experimental and procedural outcomes.
用于光子传输的蒙特卡罗方法通常用于预测光源在组织或材料内部引起的体积加热。该方法依赖于（相对于温度）恒定的光学特性，特别是散射和吸收系数。实际上，光学系数通常与温度有关，这会导致模拟结果出现误差。本研究的目的是开发一种能够纳入可变特性并准确模拟温度将大幅变化的系统的方法，例如在冷冻组织的激光解冻情况下。开发了一种数值模拟，该模拟利用蒙特卡罗方法进行光子传输，以模拟一个允许光学和热特性随温度变化的系统的热响应。这是通过将传统的蒙特卡罗光子传输与传热模拟相结合来实现的，以提供一个反馈回路，该回路根据每个时刻的当前温度选择局部特性。此外，光子步长被分段，以准确获得均匀（但非等温）材料内的路径长度。通过与使用恒定特性的已建立的蒙特卡罗模拟进行比较，以及与针对温度可变特性的比尔-朗伯定律进行比较，对模拟进行了验证。该模拟能够准确预测特性随温度变化的系统的热响应。对于激光加热硅的代表性系统，可变特性方法和恒定特性方法的结果差异可能会超过100K。该模拟将在温度发生大幅变化的材料中返回更准确的光辐照吸收结果。模拟结果中这种提高的准确性导致对活体组织的热预测更好，并可以提供更好的规划以及改善实验和程序结果。
