Controlling the Temperature on the Vein Wall Based on the Analysis of the IR Signal during Endovasal Laser Treatment

Possibility of controlling the temperature of the vein wall during endovasal laser treatment (EVLT) is investigated. The desired medical effect is achieved by the coagulation of the vein wall at the temperature of 80◦C. Heating of the vein wall is mainly due to the efficient conversion of laser radiation into heat in an optothermal fiber converter (OTFC) located at the output end of the optical fiber placed inside the vein. Titanium-containing optothermal fiber converter (TOTFC) is very promising for EVLT application due to its high efficiency in converting laser energy into thermal energy and its smooth shape that excludes perforation of the vein wall when the fiber moves inside the vein. During the endovasal laser treatment heated by laser radiation TOTFC emits an IR signal which can be used for controlling the temperature on the vein wall during endovasal laser treatment. At present study, a computer thermophysical model of the EVLT with TOTFC has been developed in the COMSOL Multiphysics 5.4 program (COMSOL Inc., Burlington, MA, USA). In the EVLT model, a laser radiation wavelength of 980 nm with an average laser power of 8–14 W to the traction speed of the optical fiber in range of 1–7 mm/s is applied. The dependence of the TOTFC temperature and the temperature on the vein wall has been numerically investigated. In accordance with Planck’s formula, the dependence of the spectral luminosity density of a blackbody simulating IR signal from TOTFC on its temperature has been determined. The spectral luminosity density in a wide range the wavelength of 0.4–20 µm, as well as in spectral ranges limited by the transmission of the quartz fiber and the sensitivity of Ge and PbS photodetectors was defined. The possibility of controlling the average power of the laser radiation depending on the magnitude of the change in the spectral luminosity density of TOTFC during EVLT is demonstrated. The results obtained can be useful in developing laser medical equipment and materials for use in vascular surgery at endovasal laser treatment. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.