Investigation of ablation efficiency and temperature distribution profile of 1940 NM thulium fiber laser on EX vivo ovine liver tissue

Abstract

In liver surgeries, lasers with different wavelengths are used to make incisions and excisions with minimal bleeding and pain. The purpose of this study is to examine the efficiency of a 1940 nm Thulium fiber laser in the incisional operation of liver tissue. Thus, the tissue ablation efficiency of this laser was calculated as a ratio of the ablated site to the total affected site at various laser scanning speed values and output powers. Additionally, the thermal damage at the surrounding tissue was evaluated with a thermal camera. To create an incision, laser light should be absorbed by the tissue. In this study, lamb liver tissue was irradiated by 1940 nm Thulium fiber laser through 600 µm bare ended optical fiber in continuous mode. The reason of using this specific laser was that, according to the literature, light in 1940 nm wavelength is highly absorbed by water molecules, which are abundant in soft tissues such as kidney. Initially, a predosimetry study was conducted to decide on the laser output power to be studied. Output powers including 0.6 W, 0.8 W, 1.0 W, 1.5 W, and 2.0 W were studied. According to the predosimetry study results, only 0.6 W and 0.8 W output powers were not able to be successful for ablation in most cases. Coagulation was observed in all of the incisions, independently of the output power. Base d on these findings, 1.0, 1.5, and 2.0 W output powers were decided to be used in the following experiments. In the actual experiments, the lesions were regularly created at a length of 2 cm. Laser output power and lesion lengths were kept constant in each application, while different scanning speeds were tested by changing the irradiation time. All the applications were performed with a single-pass. For example, 0.6 W output power was applied to a 2 cm length incision for 5, 10, and 15 seconds. Since the incision length was kept constant, the total light energy delivered to the samples was increased as the application time increased, which improved the ablation efficacy. During experiments, the temperature on and surrounding the incisions was monitored using a thermal camera. The results of this study showed that incision properties, such as deeper ablated and larger coagulated areas, were achieved when higher laser powers were used at slower laser scanning speeds compared to the other application parameters that were used in this study. However, carbonization, which is not desirable in laser incision applications, was also observed at 1.5 W and 2.0 W laser powers. Therefore, this study revealed that laser scanning speed and output power have a significant impact on ablation efficiency of 1940 nm Thulium fiber laser in liver tissue.