Stereotaxic laser brain surgery with 1940-nm Tm:fiber laser: An in vivo study

With exciting developments in fiber laser technology, studies investigating the use of lasers in neurosurgery have been increasing in the recent years. Fiber lasers are advantageous in many ways; first of all they are compact and they provide a more comfortable environment in the operating room due to feasibility of coupling laser light to different cross-sectioned fibers. Thulium fiber (Tm:fiber) lasers have been under investigation for medical applications since 2005 due to their spectral proximity to the water absorption peak.

The primary aim of this study is to investigate the thermal effects of the 1940-nm Tm:fiber laser on subcortical tissue and to examine the effects of laser parameters on laser-induced lesions. Secondarily, it is also aimed to reveal the importance of temperature monitoring during laser surgeries by investigating the effects of temperature change on the characteristics of laser-induced lesions.

Stereotaxic laser brain surgery was performed on 20 male Wistar rats, in order to investigate the thermal effects of Tm:fiber laser. During surgeries temperature changes in the subcortical tissue were observed with a t-type thermocouple for which a holder was designed to accomplish a 1 mm distance between the fiber tip and thermocouple tip. Histological examinations were performed on cresyl fast violet (CFV) stained slices under light microscopy. Photothermal effects of Tm:fiber laser on subcortical tissue were investigated in terms of ablated (removal of tissue), coagulated and edematous areas with a blinded micrograph evaluation. Relations between laser parameters, ablation efficiencies and rates of temperature changes were determined. Pearson's correlation coefficients between rates of temperature changes and ablation efficiencies, total laser damage and edematous area were calculated.

No significant adverse effects were observed during surgeries. Histological examinations revealed localized ablation surrounded by coagulation areas as well as edema. Ablation efficiencies ranged from 20% to 50% with changing laser parameters. The correlation coefficient between rates of temperature change and ablation efficiencies, total laser damage and edematous area were rather high.

In this study we show that Tm:fiber lasers seem to be useful tools in brain surgeries especially to vaporize and coagulate the tissue. It is also shown that temperature monitoring during laser surgery is very crucial and gives information about laser-induced lesion. Another take home message from this study is rather than the temperature increase, the rate of temperature change is more important. We found that if the temperature is changing in a short time interval, the extent of thermal damage can be minimized. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.