Optical Coherence Tomography for the Evaluation of Energy Seals and the Subsequent Evaluation of the Thulium Laser as a Hemostatic Instrument
thesisposted on 14.10.2021, 20:20 by Andrew J. Marques
This thesis presents the development of a system which integrates both an Optical Coherence Tomography system and a high-powered Thulium fiber laser. The system was developed in order to study the interaction between Thulium laser and tissue via Optical Coherence Tomography feedback. This was done given the Thulium laser’s theoretical potential to serve as a multipurpose surgical instrument. The core work of the thesis is divided into two sections:
1. The development of an energy seal evaluation methodology using Optical Coherence Tomography. One-hundred and four avian embryonic vessels were subjected to Thulium laser irradiation at 1942 nm and subsequently imaged. Using both structural and Doppler feedback, several biomarkers were identified and used to classify irradiation outcomes as sealed or not sealed. The methodology developed here was compared to visual methodologies. It was found that the reported seal rate was dependent on the classification methodology (p = 0.01) where visual evaluation reported 18% more seals across the entire data set. The specificity of visual evaluation was dependent on the type of non-seal classification (p < 0.0001). Given that the developed methodology relied on the identification of biomarkers rather than user opinion, an objective evaluation methodology was achieved. Hemostatic systems evaluated visually should be re-evaluated.
2. Evaluating the Thulium laser as a hemostatic instrument. Average power, exposure time, and spot size were varied to maximize the seal rate. At sub 2 s exposure times the overall seal rate across all vessels was 29%. The highest seal rate achieved for a single condition was 60%. The rupture rate showed some correlation to average power.
Biological factors were found to have a significant effect on the seal rate where the mean vessel diameter for non-seal outcomes was greater than that for seal outcomes
(p < 0.001). Tissue dehydration was a factor in this study. The average heat affected zone was 2.2 ± 1.1 mm, typical of a hydrolytic laser. This finding affirmed that hydrolytic lasers can induce seals despite the dimensions of the optical zone. As irradiance increased so did the heat affected zone, the opposite was true for exposure time. Using a dose until seal approach the seal rate was 95% across 18 vessels. The average therapeutic time was 9 ± 3 s for single vessel. Based on the overall lack of predictability observed in interactions between Thulium laser and vascular tissue, as well as the relatively poor seal rates, the Thulium laser was not recommended to be used in hemostatic applications.