Comparison of two cw infrared laser systems emitting wavelengths at 1.92 μm and 2.01 μm for tissue dissection in liver surgery

For ablation of soft tissue by laser radiation water is the main absorptive chromophore in the tissue. In this study the absorption coefficient of water at different temperatures was investigated for wavelengths at 1920 nm and 2013 nm respectively. The laser radiation was transmitted via a quartz fiber (Ø 600μm) in to a thermal isolated and heated water filled cuvette. At different temperatures the transmittance of water was measured for both wavelengths. According to Beer-Lambert's law the absorption coefficient α was calculated. At 2013 nm absorption coefficient ? of water decreases from 64.9±0.3/cm² @ 20°C to 49.7±1.2/cm² @ 80°C, while at 1920 nm α increases from 126.4±1.6/cm ² @ 20°C to 142.5±1.6/cm² @ 80°C. Histological evaluation of liver tissue showed ablated channel depth about 800 μm for 1920nm and 1700 μm for 2013 nm. Thermal damage zone was 600-770 μm for 1920 nm and 830-1380 μm for 2013 nm. For small and precise dissection of soft tissue by laser radiation in the 2 μm range the wavelength at 1920 nm should be preferred.