Shafirstein Gal, Bäumler Wolfgang, Lapidoth Moshe, Ferguson Scott, North Paula E, Waner Milton
Vascular Anomalies Center, Arkansas Children's Hospital and University of Arkansas for Medical Sciences, Little Rock, Arkansas 72202, USA.
Lasers Surg Med. 2004;34(4):335-47. doi: 10.1002/lsm.20028.
Monte Carlo (MC) simulations of light-tissue interactions and analytical solutions for the diffusion approximation theory have been used to determine the optimal laser wavelength and radiant exposure to treat port-wine stains (PWS). Both approaches suggest that optimal parameters are a wavelength of 585 or 595-nm with pulse times of 0.45-20 milliseconds. However, which parameters are optimal is still unclear. As differences in vessel size and in temperature distribution within vessels appeared to be the main reasons for the varied responses to the same laser treatments, we sought to develop a solution to the diffusion approximation in order to calculate temperature distribution and the resulting coagulation pattern within specific blood vessels.
STUDY DESIGN/MATERIALS AND METHODS: The light and heat diffusion equations were simultaneously solved with the finite element method (FEM). The latent heat of evaporation was included in the thermal analysis. The temperature and coagulation patterns across specific blood vessels, within a heterogeneous medium, were calculated for laser wavelengths of 585 and 595-nm with clinical parameters.
At 1.2 mm deep, the calculations predicted that vessels ranging from 50 to 100 microm in diameter would be coagulated from top to bottom, small vessels (10 microm) would be spared, and vessels larger than 150 microm would be partially coagulated. Coagulation across vessels was more uniform for the 595-nm than for the 585-nm wavelength. Maximal temperatures did not exceed 100 degrees C because of the inclusion of latent heat in the thermal calculations.
To study laser treatments of PWS with the diffusion approximation, FEM is an effective method to calculate the coagulation patterns within specific blood vessels. To improve coagulation efficacy at 585 and 595-nm wavelengths, the radiant exposure should be increased without increasing the irradiance.
光与组织相互作用的蒙特卡罗（MC）模拟以及扩散近似理论的解析解已被用于确定治疗葡萄酒色斑（PWS）的最佳激光波长和辐射剂量。两种方法均表明，最佳参数为波长585或595纳米，脉冲时间为0.45 - 20毫秒。然而，究竟哪些参数是最佳的仍不明确。由于血管大小差异以及血管内温度分布似乎是对相同激光治疗产生不同反应的主要原因，我们试图开发一种扩散近似的解决方案，以计算特定血管内的温度分布及由此产生的凝固模式。
研究设计/材料与方法：利用有限元法（FEM）同时求解光和热扩散方程。热分析中考虑了蒸发潜热。针对波长为585和595纳米的激光，结合临床参数，计算了异质介质中特定血管的温度和凝固模式。
在深度为1.2毫米处，计算预测直径50至100微米的血管将从上至下被凝固，小血管（10微米）将不受影响，直径大于150微米的血管将部分被凝固。595纳米波长的血管凝固比585纳米波长更均匀。由于热计算中包含潜热，最高温度未超过100摄氏度。
为用扩散近似研究PWS的激光治疗，有限元法是计算特定血管内凝固模式的有效方法。为提高585和595纳米波长的凝固效果，应在不增加辐照度的情况下增加辐射剂量。
