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

研究对象总结研究成果。为建立激光间质热疗(LIT)治疗颅内肿瘤的方法，作者研究了磁共振(MR)温度标测下激光间质照射局部温度的控制方法。方法：研究方法。研制了一套半导体激光系统和6种不同类型的光纤系统，利用水-质子化学位移技术进行磁共振温度测量。在动物实验中，用光学温度计评估磁共振测温的准确性，然后用两种激光照射方法(连续和间歇)观察温度分布的差异。在体模实验中，利用磁共振测温技术研究了不同光纤系统的温度分布特征，结果表明，在活体实验中，磁共振测温与光学温度计测温的温差为0.88℃。除漫反射纤维体系外，其余纤维体系在间隙条件下均呈球状温度分布。在高功率激光照射下，裸端光纤尖端有时会发生碳化。漫反射投射光纤系统的温度分布呈圆柱形，温度分布比裸端光纤系统的温度分布有逐渐升高的趋势。扩散投射的纤维体系尖端无碳化现象。另外，间歇照射方法对温度的逐渐升高也是有效的。改进光纤系统和间歇照射可以降低激光强度，从而将碳化风险降到最低。该技术可用于磁流变液温度测量中的温度调节。

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.