Tissue treatment under water with simultaneously fiber-guided erbium and holmium laser radiation

摘要

Abstract: Non-contact fiber guided IR-tissue treatment under water requires the formation of a water vapor channel at the fiber tip to bridge the water layer between the fiber and the tissue surface and to allow transmission of the radiation. The formation of the channel, however, consumes most of the initial pulse energy which strongly restricts the ablation efficiency. The goal of this study was to determine optimum laser parameters which guarantee a high ablation efficiency and a high cutting precision. A multi-wavelength-laser system was realized by simultaneously guiding erbium and holmium laser radiation via a single ZrF$-4$/ fiber. Both lasers were operated in free-running mode at pulse durations adjustable between 100 $mu@s and 1 ms. Pressure measurements and video flash photography were performed to study the channel formation process as a function of laser wavelength, pulse duration and delay time between laser pulses at different wavelengths. The tissue response of human meniscus after laser impact was histologically investigated. The efficiency of erbium laser tissue ablation under water increases from 25% up to 80% by using a multi-wavelength system emitting 2.1 $mu@m and 2.79 $mu@m radiation. This is achieved when a 200 $mu@s long holmium laser pulse of low energy is used to open a water vapor channel through which the ablating erbium laser radiation can be transmitted. The induced thermal tissue damage is essentially determined by the holmium laser parameters and the delay time between both pulses. The combination of erbium and holmium laser radiation offers the surgeon the possibility for efficient and precise cutting of tissue under water. Moreover, it represents an universal medical instrument for cutting and/or coagulation just by changing the laser parameters without changing the instrument.!15