Laser ablation of bone tissue with Q-switched infrared laser sources for neurosurgical applications
For specific indications in neurosurgery, such as the removal of brain tumors in eloquent locations and the deep brain stimulation, awake craniotomy offers multiple advantages. However, due to the severe discomfort experienced during burr-hole drilling, patients are hesitant to opt for awake craniotomy. Laser systems provide an alternative to surgical drills as a silent and vibration-free bone cutting method. Until now no laser system achieved adequate ablation rates (> 2:5mm3/s) at sufficiently high aspect ratio (>5) to fulfill the requirements for craniotomy. The aim of this study is to investigate the ablation of bone tissue under the needs for neurosurgery using three different Q-switched infrared laser sources assisted by a water spray system. One of the laser sources is a commercial Q-switched CO2 laser system operating at 10:6 mm with a pulse energy of 4 mJ. In addition, two in-house developed, short-pulsed IR-laser sources operating at 2:91 mm (Cr:ZnSe) with a pulse energy of 0:76mJ and at 1:9 mm (Tm:YLF) with a pulse energy of 2:2mJ are investigated. The results show that highly efficient bone ablation with the CO2 laser at rates of 6mm3/s is possible without carbonization. With an ablation strategy using the effect of multiple reflections inside the kerf an aspect ratio of 17 was achieved for narrow incisions at widths smaller than 100 mm. Another ablation strategy shows a twofold higher ablation depth shifting the laser focus stepwise into propagation direction. Even though a high ablation efficiency can be achieved with the Cr:ZnSe laser source and the CO2 laser source, the Cr:ZnSe laser cannot fulfill the required ablation rates. The CO2 laser shows a fast ablation in significant depth with a maximum depth of 7 mm. Further investigations will concentrate on increasing the ablation depth to 10 mm.