Comparison of Er: YAG and 9.6-μm TE CO2 lasers for ablation of skull tissue

Background and Objective: Craniotomy by using a drill and saw frequently results in fragmentation of the skull plate. Lasers have the potential to remove the skull plate intact, simplifying the reconstructive surgery. Study Design/Materials and Methods: Transverse-excited CO₂ lasers operating at the peak absorption wavelength of bone (λ = 9.6 μm) and with pulse durations of 5-8 μsec, approximately the thermal relaxation time in hard tissue, produced high ablation rates and minimal peripheral thermal damage. Both thick (2 mm) and thin (250 μm) bovine skull samples were perforated and the ablation rates calculated. Results were compared with Q-switched and free-running Er:YAG lasers (λ = 2.94 μm, τ_p = 0.5 μsec and 300 μsec). Results: The CO₂ laser produced ablation rates of up to 60 and 15 μm per pulse for thin and thick sections, respectively, and perforated thin and thick sections with fluences of less than 1 J/cm² and 6 J/cm², respectively. There was no discernible thermal damage and no need for water irrigation during ablation. Pulse durations ≥ 20 μsec resulted in significant tissue charring, which increased with the pulse duration. Although the free-running Er:YAG laser produced ablation rates of up to 100 μm per pulse, fluences of 10 J/cm² and 30 J/cm² were required to perforate thin and thick samples, respectively, and peripheral thermal damage measured 25-40 μm. Conclusion: In summary, the novel 5- to 8-μsec pulse length of the TE CO₂ laser is long enough to avoid a marked reduction in the ablation rate due to plasma formation and short enough to avoid peripheral thermal damage through thermal diffusion during the laser pulse. Furthermore, in vivo animal studies with the TE CO₂ laser are warranted for potential clinical application in craniotomy and craniofacial procedures.