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

研究结果总结为了确立激光间质热治疗（LITT）作为颅内肿瘤的一种治疗方式，作者研究了一种在磁共振（MR）温度定位下通过间质激光照射控制局部温度的方法。方法。为此研制了一种二极管激光系统和6种不同类型的光纤系统。采用水质子化学位移技术进行磁共振测温。在动物实验中，用光学体温计估计MR温度测量的精度，然后用连续和间歇两种激光照射方法观察温度分布的差异。在模体实验中，利用磁共振测温技术研究了各光纤系统的温度分布特征。结果表明，磁共振温度监测与光学温度计测量的体内温度差异为0.88℃。除漫射投影光纤系统外，所有光纤系统在间隙条件下均形成球形温度分布。在高功率激光照射下，光纤裸端针尖周围有时会发生碳化现象。漫射投影光纤系统的温度分布呈圆柱状，温度分布曲线较裸端光纤系统呈现逐渐升高的趋势。纤维系统顶端未发生炭化，用于漫射投影。此外，间歇照射法也可使温度逐渐升高。光纤系统改造和间歇性照射可降低激光束强度，从而降低碳化的风险。我们的技术可以作为一种有用的方法，用于在MR温度测量下的LITT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.