Guidance of hard tissue ablation by forward-viewing optical coherence tomography

A key issue in laser surgery is the inability for the human operator to stop the laser irradiation in time while cutting/ablating delicate tissue layers. In the present work, we forward-image through the laser machining front in complex biological tissue (dense bovine bone) to monitor the incision's approach to subsurface interfaces in real-time (47-312 kHz line rate). Feedback from imaging is used to stop the drilling process within 150 micron of a targeted interface. This is accomplished by combining the high temporal and spatial resolution of infrared optical coherence tomography (OCT) with a robust, turn-key, high brightness fiber laser. The high sensitivity of the imaging system (~100 dB) permit imaging through the rapidly changing beam path even with the additional scattering caused by the thermal cutting process. In spectral-domain OCT, the imaging acquisition period is easily locked to the machining laser exposure. Though motion-induced artifacts reduce interface contrast, they do not introduce incorrect depth measurements as found in other OCT variants. Standard tomography imaging of the tissue (B-scans) is also recorded in situ before and after laser processing to highlight morphology changes.