Jia Hao, Chen Bin, Li Dong
State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, China.
Lasers Med Sci. 2017 Apr;32(3):513-525. doi: 10.1007/s10103-017-2143-8. Epub 2017 Jan 13.
Laser treatment is the most effective therapy in dermatology for vascular skin disorders, such as port-wine stains (PWS). Changes in heat-induced absorbance in blood must be determined for accurate numerical simulation and implementation of multi-pulse laser therapy for treatment of PWS. Thermally induced absorbance changes in hemoglobin in blood were compared in vitro between slow water bath heating and fast heating irradiated by using sub-millisecond Nd:YAG laser. Blood composition at different temperatures was calculated by comparing blood absorption spectra with those of pure HbO, Hb, and metHb at room temperature. Blood absorbance to heat energy were categorized into three stages distinguished by metHb and coagulation points, which are the validity and security thresholds of the optimized therapy, respectively. Rapid laser heating can distinctively enhance blood absorbance by photochemically induced strong instability compared with slow heating at a constant temperature. Slow heating facilitates metHb point at 70 °C and coagulation point at 75 °C as the temperature of the water bath increases. However, the temperature at which metHb or coagulation point shifts to higher than 10 °C when pulses and fluence in laser irradiation change. Laser fluence less than 20 J/cm and more than 50 J/cm is unsuitable for laser treatment because of its low probability to coagulate vascular hyperplasia and high probability to damage normal tissues adjacent to target lesions, respectively. Few bubbles formed after mediate fluence is beneficial to minimize adverse side-effects. Considering blood absorbance, temperature evolution, and bubble formation, we recommend 30-40 J/cm and 2-4 Hz frequency as the optimal laser parameters in sub-millisecond Nd:YAG laser.
激光治疗是皮肤科治疗血管性皮肤病（如葡萄酒色斑，PWS）最有效的疗法。为了对PWS的多脉冲激光治疗进行精确的数值模拟和实施，必须确定血液中热诱导吸光度的变化。通过亚毫秒级钕：钇铝石榴石激光照射，比较了体外慢水浴加热和快速加热时血液中血红蛋白的热诱导吸光度变化。通过将不同温度下的血液吸收光谱与室温下纯氧合血红蛋白（HbO）、血红蛋白（Hb）和高铁血红蛋白（metHb）的吸收光谱进行比较，计算了不同温度下的血液成分。血液对热能的吸光度分为三个阶段，分别以metHb和凝固点为特征，这两个点分别是优化治疗的有效性和安全性阈值。与恒温慢加热相比，快速激光加热可通过光化学诱导的强不稳定性显著提高血液吸光度。随着水浴温度升高，慢加热有利于在70°C时达到metHb点，在75°C时达到凝固点。然而，当激光照射的脉冲数和能量密度发生变化时，metHb或凝固点的温度会升高至高于10°C。激光能量密度小于20 J/cm²和大于50 J/cm²分别由于凝固血管增生的可能性低和损伤靶病变周围正常组织的可能性高，而不适用于激光治疗。中等能量密度照射后形成的气泡较少，有利于将副作用降至最低。综合考虑血液吸光度、温度变化和气泡形成，我们推荐30 - 40 J/cm²和2 - 4 Hz的频率作为亚毫秒级钕：钇铝石榴石激光的最佳激光参数。
