The impact of the laser fiber-tissue distance on histological parameters in a porcine kidney model.

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.