Novel laser system and laser irradiation method reduced risk of carbonization during laser interstitial thermotherapy : Assessed by MR temperature measurement

研究成果总结。为了建立激光间质热疗（LITT）作为颅内肿瘤的治疗方式，作者研究了磁共振（MR）温度图下激光间质照射局部温度控制方法。方法.研制了一套半导体激光器系统和6种不同类型的光纤系统，并采用水质子化学位移技术进行了磁共振测温。在动物实验中，首先用光学温度计测量MR温度，然后观察两种激光照射方式（连续和间歇）下温度分布的差异。在体模实验中，利用MR测温技术研究了各光纤系统的温度分布特征，结果表明，在体MR测温与光学测温的温度差为0.88℃。在间隙条件下，除漫投影光纤系统外，所有光纤系统的温度分布均为球形。在高功率激光辐照下，光纤裸端尖端有时会发生碳化。漫反射光纤系统的温度分布呈圆柱形，且温度分布比光端光纤系统的温度分布呈现逐渐升高的趋势。弥散投影时，纤维系统尖端无碳化现象。此外，间歇辐照法也有利于温度的逐步升高。光纤系统的改进和间歇照射可以降低激光束强度，从而将碳化风险降至最低。我们的技术可以在MR温度测量下的LITT过程中的温度调节的有用的方法。

Summary of research results Object. To establish of laser interstitial thermotherapy (LITT) as a therapeutic modality for intracranial tumors, the authors investigated a control method of local temperature by interstitial laser irradiation under magnetic resonance (MR) temperature mapping. Methods. A diode laser system and 6 different types of optical fiber system were developed for LITT.The water proton chemical shift technique was used for MR temperature measurement. In animal experiments, the accuracy of MR temperature measurement was estimated with a optical thermometer, then difference of the temperature profile was observed by two laser irradiation methods (continuous and intermittent). In phantom experiments, character of the temperature profile by each fiber system was investigated with MR temperature measurement.Our results showed the difference of the temperature between MR temperature monitoring and optic thermometer measurement was 0.88℃ in-vivo. All fiber systems except for the diffuse projection fiber system made a spherical temperature profile under interstitial condition. With high power laser irradiation, a carbonization was sometimes occurred around the bare end fiber tip. The diffuse projection fiber system made a cylindrical temperature distribution, and the temperature profile showed a gradual temperature elevation than the bare end fiber system. No carbonization was occurred at the tip of fiber system for diffuse projection. In addition, intermittent irradiation method also worked for a gradual temperature elevation. Fiber system modification and intermittent irradiation works for reducing the laser beam intensity, then these should work to minimize the risk of carbonization.Conclusion. Our techniques can be useful method for temperature regulation during LITT under MR temperature measurement.