Automated 3D bone ablation with 1,070 nm ytterbium-doped fiber laser enabled by inline coherent imaging.

Abstract

Laser osteotomy bears well-identified advantages over conventional techniques. However, lack of depth control and collateral thermal damage are barriers to wide clinical implementation. Flexible fiber delivery and economical benefits of ytterbium-doped fiber lasers make them desirable for laser osteotomy. In this work, we demonstrate automated bone ablation with a 1,070 nm industrial-scale fiber laser to create 3D target structures with minimal thermal side-effects. Fresh and dry ex vivo cortical bone samples are ablated using 50-100 µs laser pulses of 15-30 mJ. In situ inline coherent imaging monitors ablation dynamics with micron precision and on microsecond timescales. Ablation depth is extracted by on-the-fly processing of ICI data, enabling feedback control of depth (via laser pulse number). Final ablated morphology, measured by an ex situ stylus profiler, is compared to the target shape. Histological examination is performed to quantify the thermal side-effects of laser ablation. Percussion drilled hole depth is highly variable for fixed laser parameters (880 ± 151 µm on fresh bone and 1038 ± 148 µm on dry bone) due to nondeterministic ablation. ICI-enabled depth control is implemented to achieve precise ablation of complex 3D features. The RMS deviation between target and ablated morphology is 12.6 µm. The heat-affected zone is found to be 5-10 µm on fresh and dry bone. An ytterbium-doped fiber laser is utilized for cortical bone ablation with limited thermal side-effects. In situ real-time ICI measurement enables characterization of bone ablation dynamics. Furthermore, ICI closed-loop feedback realizes depth-controlled ablation on heterogeneous bone. This proof-of-principle study shows great promise for ICI-guided laser osteotomy.