Development of miniaturized long-range optical coherence tomography for smart laser surgery system

Optical coherence tomography (OCT) is a well-established interferometric imaging technology in biology and medicine. Nowadays, OCT has many applications in different clinical specialties due to its capability to provide high-resolution three-dimensional images of biological tissue in real time and remotely. In addition to the main application of OCT as a non-invasive optical biopsy, its features make it an ideal candidate as a visual-feedback system during laser surgery. OCT-assisted laser surgery can compensate for the primary inherent drawback of laser-surgery systems, namely, their feedback. In this thesis, a long-range OCT system was developed to provide the required feedback for surgeons during laser osteotomy.
In the first part of this thesis, a long-range and extended DOF swept-source OCT system (SS-OCT) was developed. The long-range SS-OCT system demonstrated an imaging range of 26.2 mm and an extended DOF of 28.7 mm. The custom-made OCT system was integrated with an Er:YAG laser to monitor and control the depths of laser-induced cuts in real-time. In addition to the real-time visual feedback, a tissue-sensor (LIBS) system was integrated with an Er:YAG laser to achieve closed-loop laser osteotomy. The closed-loop system allowed tissue-selective laser surgery with a controlled ablation depth in the target tissue (bone).
Thermal damage during bone surgery is a drawback of mechanical and laser methods. For this reason, the next goal of the thesis was to investigate the potential of a phase-sensitive OCT system to monitor temperature increases in the tissue during laser osteotomy. The developed method is based on calibrating the photothermal expansion of tissue with its corresponding temperature increase. The preliminary results of the phase-sensitive OCT system show its potential to monitor temperature increases in bone tissue beyond the coagulation level.
In the last part of this thesis, a miniaturized prototype of the fiber-based Er:YAG laser and OCT system were designed and fabricated. The miniaturized, integrated setup could potentially be used in minimally invasive laser surgery. The developed system could perform several preplanned ablation cuts (maximum ablation depth of 5 mm) with the assistance of the real-time depth monitoring provided by the OCT system. This study was part of the MIRACLE project, which aims to develop a robotic endoscope for performing laser-based bone surgery.