This study aims to optimize the ablation depth using a Ho:YAG laser and a waterjet. The results show that the maximum achieved depth for a 1 cm-long line cut was 0.86, 1.07, and 2.24 mm at energies of 500, 1000, and 2000 mJ/pulse, respectively. The line cuts were performed by translating the sample horizontally (back and forth) at the speed of 8 mm/s. After 120 s (~100 pulses/position), the depth achieved was saturated at all energy levels. As Ho:YAG lasers can be delivered through low-cost and flexible silica fibers, they have a great potential for endoscopic minimally invasive surgeries.
We investigated phase-sensitive optical coherence tomography's performance to monitor the dynamic changes during controlled heating of the bone. The results demonstrated the potential of this method to be used as feedback for the irrigation system.
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.
Automatic tissue classification using optical coherence tomography (OCT) explores the possibility to control laser ablation in prevention for collateral damage of critical tissues. During ablation, tissue experience thermal dissipation which induces mechanical expansion and optical properties alteration. We reconstructed OCT images of bone, fat, and muscle tissues for pre and post ablation temperatures condition using Monte Carlo simulation. We trained a deep neural network to recognize tissue type based on reconstructed OCT images with pre-ablation temperature condition and tested it on post-ablation temprature condition. The reconstructed images show small changes in the tissue structure but do not significantly affect the performance of the classifier.
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.
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