Picosecond laser procedures to enhance the efficacy of tissue resection
Mohanan, Syam Mohan P. C.
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The fundamental goal of this work was to develop an improved surgical modality in tissue, where minimising thermal damage is paramount, using an ultrashort pulse picosecond laser. Additionally, an investigation into flexibly delivering such pulses via a hollow core negative curvature fibre, in order to enable future minimally invasive endoscopic procedures, was conducted. Initially, the analysis of colon tissue resection in a porcine model based on plasma mediated laser ablation (at 1030 nm and 515 nm) using a scanning galvanometer is presented. A minimal thermally damaged region (<60 µm) and the ability to finely tune the depth of ablation using different scanning strategies, pulse repetition rate, pulse energy and laser fluences are demonstrated. These desirable surgical effects on the tissue were confirmed using surface profilometry and histological analysis. The picosecond laser ablation of healthy and cancerous lung tissue in an ovine model was also investigated. It has been observed that the ablation depth of cancerous tissue is approximately equal to half of the ablation depth of healthy tissue using the same laser parameters. This thesis also demonstrates that secondary effects of plasma formation such as shock wave induced mechanical damage, cavitation/gas bubble formation, can occur dependent on the parameters used. An appropriate scanning strategy (where there is little or no overlap between consecutive laser pulses) therefore needs to be implemented to minimise these detrimental effects. A laser scanning methodology (0% and 20% overlap with consecutive pulses) with enhanced reduction in thermal injury is presented using 20 kHz pulse repetition rate, 1030 nm wavelength and 13 J/cm2 laser fluence with a maximum ablation rate of 6 (0% Overlap) and 4 (20% overlap) mm3 /minute. The development of novel hollow core microstructured fibres has enabled the potential for delivery of ultrashort pulse picosecond laser radiation throughout the body. Therefore, in this thesis ultrashort laser pulses suitable for precision porcine colon resection were flexibly delivered via a hollow core negative curvature fibre. The fibre was manipulated via multi-axis robotic device to mimic movements expected during a practical surgical procedure. Again, a controllable change in ablation depth and with a minimum thermally damage region (< 85 µm) is observed. Furthermore, ablation depths are of comparable scale to that of early stage lesions/polyps in the inner lining of the colon and hence provide a level of control of resection suited to surgical application to thin walled structures such as the bowel.