Lasers have introduced many advantages to the medical field of osteotomy (bone cutting), however, they are not without drawbacks. The thermal side effects of laser osteotomy, in particular, affect a patient’s healing process. Employing an irrigation system during surgery is a standard solution for reducing thermal damage to the surrounding tissue, but, due to the high absorption peak of water at the wavelength of Er:YAG laser (2.96 μm), accumulated water acts as a blocking layer and reduces the ablation efficiency. Therefore, irrigation systems would benefit from a high-speed and accurate feedback system to monitor the temperature changes in the tissue of interest. Phase-sensitive optical coherence tomography (PhS-OCT) is a highly sensitive method for measuring internal displacement (photothermal-induced expansion) during laser surgery. In this study, we utilized the integrated swept source PhS-OCT system (operating at a central wavelength of 1314 nm and with an imaging-speed of 104,000 A-scans/s) with an Er:YAG laser to detect localized phase changes induced by laser ablation irradiation and thereby quantify the photothermal-induced expansion of bone. The PhS-OCT system was calibrated by measuring the phase changes corresponding to the displacement of cover glass attached to a piezoelectric actuator (PA4HEW, Thorlabs) at different operating voltages. Furthermore, we explored how the induced photothermal expansion of bone changes when irradiated by different pulse energies. Using a PhS-OCT system to spatially and temporally resolve measurements of axial displacement of bone during laser surgery can play an important role in determining the corresponding temperature map, which can, in turn, offer feedback to the irrigation system in smart laser osteotomy.
Optical Coherence Tomography (OCT) has been proven to be a precise monitoring tool for laserosteotomy which can provide three-dimensional, high resolution and real-time images of a target sample. However, the main technical drawback of utilizing OCT as a monitoring system for laser ablation is the limited imaging range. In this paper, we reported a prototype where we integrated a long-range swept-source OCT system (3.3cm imaging range in the air) with an Er:YAG laser for ablation. We demonstrated that the integrated system can monitor the ablation of bone by Er:YAG with varying pulse energy levels and durations.
The main purpose of this study is to evaluate the performance of different optical fibers after coupling an Er:YAG laser through them. This allows us to evaluate the feasibility of using them in future for minimally invasive ablation of bone, where a fiber has to be guided inside an endoscopic device. We coupled a high-power Er:YAG laser (λ = 2.94 μm) in different fibers separately. We analyzed the features and benefits of each fiber during the coupling process. The laser was operated at repetition rates of 1, 5, and 10 Hz in the energy range of 10-830 mJ. We used hollow-core, fluoride, sapphire and germanium oxide fibers with core sizes of 500, 450, 425 and 450 μm, respectively. The coupling efficiencies were determined by comparing the measured input and output energies for all the fibers. The resistance of each fiber to the input energy was evaluated by monitoring the stability of the measured output energy over time. From our observations, the coupling efficiencies for all the fibers were in the range 70 to 81 %. Due to the high coupling efficiency, all fibers have the potential to be used in endoscopic applications. However, their use will mostly depend on the individual need of a specific application.