gms | German Medical Science

Objective: Surgical bone removal relies on mechanical instruments with inherent limitations (drills, rongeurs). Currently available laser systems generate heat to remove tissue. Advances in laser ultra-short pulsed technology enable a plasma induced cold ablation process without vibration and acoustic sound. We investigated picosecond laser radiation to remove bone in combination with optical coherence tomography (OCT) to continuously monitor the ablation process for precise voxel based bone cutting.

Methods: A picosecond laser with a maximum average power of 200 W and 200 kHz repetition rate was used to perform a plasma induced ablation process. During the ablation the laser beam is focused by a f-theta lens with a focal length of 160 mm. A galvanometer scanner is moving the laser focus along the kerf in the bone. The process energy is applied in short laser pulses of discrete amount E_p ≤ 1 mJ and a pulse duration of τ ≤ 20 ps, whereas a single laser pulse causes a defined ablation volume (voxel) of micrometer dimensions. The whole kerf of the laser cutting process can be fragmented into a 3D-grid of voxels. The bone tissue is ablated in a digital manner addressing voxel by voxel with the scanned laser focus. The cutting process is monitored with a high speed 80 kHz OCT system. This delivers a 3D-real time map of the kerf and the residual bone thickness. Laser cutting experiments were performed on bovine bones.

Results: We developed a handpiece with integrated compact galvanometer scanner, focusing optics, OCT sensor and rinsing system to remove ablated tissue and blood out of the process volume. In total 138 laser cutting experiments resulted in a bone removal rate with infrared laser light (l = 1030 nm) of dV/dt = 2.5 mm³/s for a laser power of P = 130 W. Histologically there was no carbonization at the borders of resection.

Conclusion: The availability of ultra-short pulsed lasers opens new possibilities of ablation procedures in neurosurgery such as precise bone removal without heat, vibration and acoustic sound. A handpiece with integrated compact galvo scanner and OCT sensor allows for a voxel based cutting of a predefined 3D geometry with a real time cutting control by an OCT sensor. Applications include bone removal in spine surgery, awake surgery (Deep Brain Stimulation, tumor resection) and skull base surgery.

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