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

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Abstract
Background and Objective: To establish laser interstitial thermotherapy (LITT) for intracranial tumors, the authors investigated a method to regulate localized temperature generated by interstitial laser irradiation using magnetic resonance (MR) temperature mapping.Study Design/Materials and Methods: A diode laser system and six different types of optical‐fiber system were developed for LITT. The characteristics of temperature profiles produced by each laser‐fiber system were investigated with MR temperature measurement (the water proton chemical technique), and differences in the temperature profile induced by two laser‐irradiation methods (continuous and intermittent) were observed.Results: All fiber systems with the exception of the diffuse‐projection fiber system, created a spherical temperature profile. Carbonization sometimes occurred around the bare‐end fiber tip upon high power laser irradiation. The diffuse‐projection fiber system produced a cylindrical temperature distribution, and the temperature profile showed a more gradual temperature elevation than the bare‐end fiber. No carbonization occurred at the tip of the diffuse‐projection fiber system. In addition, the utilization of the intermittent irradiation method also increased temperature gradually. Fiber‐system modification and intermittent irradiation reduced laser‐beam intensity and the risk of carbonization.Conclusion: The use of a diffuse‐projection fiber system which intermittently transmits a reduced intensity laser beam is an effective tool to regulate temperature during LITT using MR temperature measurement. Lasers Surg. Med. 29:108–117, 2001.