Optics and thermodynamics of titanium-containing optothermal fiber converter and vein wall during endovasal laser coagulation
Endovasal laser coagulation (EVLA) is a modern promising method for treating varicose veins, in which a fiber is inserted into a vein through a puncture, and as a result of exposure to laser radiation during the movement of the fiber, the varicose vein will collapse . Many types of converters are placed on the distal end of optical fiber for effective transformation laser radiation to the heat . The titanium-containing optothermal fiber converter (TOTFC) showed good response of the temperature of the vein wall to achieve the collapse . Laser radiation with different wavelengths such as 532nm, 810nm, 980nm, 1064nm, 1310nm, 1470nm, 1910nm, 2100nm are used for endovasal laser coagulation . During endovasal laser coagulation, control of initial parameters such as laser power, laser wavelength and the traction speed of the converter are necessary.
As the current study, literary data analysis was carried out and a model of interaction titanium-containing optothermal fiber converter with a vein was built. Optical modeling was performed by Monte Carlo in the "TraceProExpert 7.0.1 Release" ("Lambda Research Corporation"; USA). Thermal modeling was performed in the software package "COMSOL Multiphysics" ("COMSOL Inc.", USA; version number 5.4).
The optical parameters of the titanium-containing optothermal fiber converter are calculated, and measurements of its absorption are performed. As a result of the optical calculation, the distribution of absorbed light with different wavelengths around TOTFC placed in vein was obtained. It was demonstrated that radiation with wavelengths of 532nm, 1470nm, 1910nm and 2100nm is concentrated near the converter, while radiation with wavelengths of 810nm, 980nm, 1064nm and 1310nm reaches the vein walls.
As a result of the thermal calculation, the dependence of the vein wall temperature on the distance between the converter and the vein wall at constant power of diode laser radiation with different wavelengths, as well as the dependence of the temperature of the vein wall on the laser power were determined. The effect of traction speed of the converter on the temperature of the vein wall has been assessed. The effect of wavelength of laser radiation on the temperature of the vein wall has been investigated also. The significant effect of the laser radiation wavelength on the temperature of the vein wall was not found. It is shown that at the traction speed of the TOTFC with 9-10W of 980nm diode laser radiation equal to 2 mm/s the walls of the vein can be heated up to 80 °C and above, which is enough to collapse a vein.
The results of the study suggest that titanium-containing optothermal fiber converter could be a good choice during endovasal laser coagulation.
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Do Thanh Tung
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