Effect of optical fiber diameter and laser emission mode (cw vs pulse) on tissue damage profile using 1.94 µm Tm:fiber lasers in a porcine kidney model.

PURPOSE: To evaluate the ablation capacity using two Thulium fiber lasers (TFL) in a porcine kidney model.
METHODS: All tissue samples were mounted on a motorized stage for a precise speed of cutting. A continuous wave (cw) TFL and a super pulsed (SP) TFL were used at power settings of 60 and 120 W with 200 and 600 µm laser fibers. After lactate dehydrogenase staining, histological evaluation was performed to measure the vaporization volume (VV), ablation depth (AD), thermo-mechanical damage zones (TMZ), coagulation zones (CZ) and the carbonization grade (CG).
RESULTS: At 120 W, no significant differences were seen between 200 and 600 µm fibers utilizing the cw TFL regarding VV (24.6 vs. 28.2 mm3/s), AD (5.6 vs. 5.7 mm), TMZ (0 vs. 0 mm2) and CZ (18.1 vs. 12.3 mm2). Using the SP TFL, no significant differences between both fiber diameters with regard to VV (4 vs. 6.2 mm3/s), AD (2.7 vs. 3.4 mm), TMZ (1 vs. 2.6 mm2) and CZ (3.1 vs. 2.2 mm2) at 120 W were found, respectively. However, the VV of the cw TFL at 60 W was significantly less compared to 120 W using 200 and 600 µm fibers, respectively, whereas the SP TFL did not show significant differences between 60 and 120 W with regard to VV. SP TFL showed a consistently lower CG compared to cw TFL.
CONCLUSIONS: This experiment suggests that there is no significant difference using 200 or 600 µm laser fibers in cw or SP TFLs. However, the cw TFL produces a coagulation zone three to five times larger than the SP TFL regardless of the fiber diameter.