Purpose: To evaluate the impact of the fiber-tissue distance on histological parameters in a porcine kidney model.
Methods: Four lasers were tested at 60 W using a 600-µm bare-ended fiber: a continuous wave (cw) thulium fiber laser (TFL), a super pulsed (SP) TFL, a Ho:YAG laser, and a blue diode laser (BDL). All tissue samples were mounted on a motorized XY-translation stage. The fiber-tissue distance was changed within a range from 0to 6 mm. Ten incisions were made with each laser at each distance. Afterwards, the tissue samples were sliced with a microtome for lactate dehydrogenase staining to determine zones of thermal damage.
Results: In contact mode, the largest incision depth was found for the cw TFL (1.7 ± 0.1 mm) compared to the SP TFL (1.0 ± 0.1 mm), BDL (0.9 ± 0.1 mm) and HoYAG laser (1.1 ± 0.1 mm), respectively. With regard to the coagulative properties, the SP TFL and the Ho:YAG laser showed comparable coagulation depths with 0.7 ± 0.1 and 0.6 ± 0.1 mm, respectively. At 2 mm fiber-tissue distance, the Ho:YAG laser was the only laser that vaporized tissue (incision depth: 0.2 ± 0.1 mm). The BDL was the only laser that caused coagulation at a distance of 3-5 mm.
Conclusion: Our results support the clinical observation that cw TFL must be defocused for best coagulation, while the coagulation depth of the SP TFL remains nearly constant within the range of 0-3 mm. Increasing the distance of the laser fiber to the tissue up to 5 mm did not cause significant differences with regard to coagulation depth using the BDL.
Keywords: Blue diode laser; Ex vivo; Laser; Porcine kidney; Thulium fiber laser.