Photothermal ablation of liver tissue with 1940-nm thulium fiber laser: Ablation efficiency and temperature measurements

The purpose of this study was to investigate the effectiveness of 1940-nm Thulium fiber laser for liver surgery. This was done by determining the ablation efficiency of different working modes and power settings of 1940-nm Thulium fiber laser on liver tissue, in addition to utilizing a real time temperature monitoring to provide the necessary feedback for adjusting laser parameters to minimize the collateral thermal damage to adjacent tissues. Thulium fiber laser was delivered to lamb liver tissue samples via 400 $\mu$m flat-cut bare-ended tip fiber in contact mode. Continuous-wave and pulsed modes were used, each at 4 different laser power values (200, 400, 600, and 800 mW) and exposure times. Exposure times were chosen to give the same total applied energy of 4J for comparison purposes. A total of 64 laser applications were performed in order to study 8 laser parameter combinations with each parameter combination repeated 8 times. Following laser irradiation, tissues were processed and stained with H\&E for macroscopic evaluation of ablation and total altered areas, and ablation efficiencies were calculated. Temperature of the nearby tissue was measured using a K-type thermocouple that was inserted at a distance of 1 mm from the fiber, and rate of temperature change was calculated. A strong correlation between the rate of temperature change and ablation area was depicted. Larger ablation and total altered areas were obtained for higher power values for both continuous-wave and pulsed modes, while ablation efficiencies were not significantly different. Continuous mode yielded higher ablation and total altered areas, and higher ablations efficiencies than pulsed mode. Histological evaluation revealed a narrow vacuolization zone and negligible carbonization for higher power values.