Paul Anup, Narasimhan Arunn, Kahlen Franz J, Das Sarit K
Heat Transfer and Thermal Power Laboratory, Department of Mechanical Engineering, IIT Madras, Chennai, Tamilnadu 600036, India.
Department of Mechanical Engineering, University of Cape Town, Rondebosch 7701, Republic of South Africa.
J Therm Biol. 2014 Apr;41:77-87. doi: 10.1016/j.jtherbio.2014.02.010. Epub 2014 Feb 15.
During laser-assisted photo-thermal therapy, the temperature of the heated tissue region must rise to the therapeutic value (e.g., 43°C) for complete ablation of the target cells. Large blood vessels (larger than 500 micron in diameter) at or near the irradiated tissues have a considerable impact on the transient temperature distribution in the tissue. In this study, the cooling effects of large blood vessels on temperature distribution in tissues during laser irradiation are predicted using finite element based simulation. A uniform flow is assumed at the entrance and three-dimensional conjugate heat transfer equations in the tissue region and the blood region are simultaneously solved for different vascular models. A volumetric heat source term based on Beer-Lambert law is introduced into the energy equation to account for laser heating. The heating pattern is taken to depend on the absorption and scattering coefficients of the tissue medium. Experiments are also conducted on tissue mimics in the presence and absence of simulated blood vessels to validate the numerical model. The coupled heat transfer between thermally significant blood vessels and their surrounding tissue for three different tissue-vascular networks are analyzed keeping the laser irradiation constant. A surface temperature map is obtained for different vascular models and for the bare tissue (without blood vessels). The transient temperature distribution is seen to differ according to the nature of the vascular network, blood vessel size, flow rate, laser spot size, laser power and tissue blood perfusion rate. The simulations suggest that the blood flow through large blood vessels in the vicinity of the photothermally heated tissue can lead to inefficient heating of the target.
在激光辅助光热疗法中，为了完全消融靶细胞，受热组织区域的温度必须升至治疗值（例如43°C）。位于受辐照组织处或其附近的大血管（直径大于500微米）对组织中的瞬态温度分布有相当大的影响。在本研究中，使用基于有限元的模拟预测了激光照射期间大血管对组织温度分布的冷却效应。假设入口处有均匀流动，并针对不同的血管模型同时求解组织区域和血液区域中的三维共轭传热方程。基于比尔-朗伯定律的体积热源项被引入能量方程以考虑激光加热。加热模式取决于组织介质的吸收和散射系数。还在有和没有模拟血管的情况下对组织模拟物进行了实验，以验证数值模型。在激光照射恒定的情况下，分析了三种不同组织-血管网络中热显著血管与其周围组织之间的耦合传热。获得了不同血管模型和裸组织（无血管）的表面温度图。瞬态温度分布因血管网络的性质、血管大小、流速、激光光斑大小、激光功率和组织血液灌注率而异。模拟结果表明，光热加热组织附近的大血管中的血流会导致对靶标的加热效率低下。
