Research On Thermal Field Of Gas Cooled Microwave Caner Ablation

Microwave ablation is one of the main methods for the treatment of tumors.It has many advantages,such as convenience in use,high reliability and low cost.It has been widely used in clinic.However,there are some problems in microwave ablation technology: microwave is near-field radiation,radiation energy concentration leads to local heating up quickly,short period of time near the radiator tissue carbonization,the formation of thermal resistance of carbonized tissue heat transfer and reduce microwave radiation efficiency,while carbonized tissue may weak radiation.At the same time,the antenna keeps hot during ablation,that may hurt the normal tissue around the probe.In order to solve the problems,the design of internal cooling pipe in the microwave ablation probe is studied.The effect of air cooling on the antenna temperature,tissue charring and ablation area are discussed.The main contents of this paper are as follows:The COMSOL simulation software was used to establish the gas-cooled microwave ablation model.The simulation of the gas-cooled microwave ablation process was carried out with no cooling,2MPa,3MPa,4MPa nitrogen gas pressure.The model is characterized by the coupling of electromagnetic field and biological heat transfer,and the 2D axisymmetric model structure simplifies the computational complexity of the model.The analysis of the specific absorptivity showed that the microwave antenna was the highest point of the temperature at the slot.The analysis of the damaged tissue showed that there was no reduction in the radial ablation area and 40% reduction in the area of the axial needle channel.The carbonized tissue analysis.The results show that the maximum temperature of the surface of the probe decreases by 63.3%,and the difference of the internal temperature of the probe does not exceed 1 ℃.The temperature of 170 ℃ is the carbonization temperature.The simulation study provides guidance for the temperature measurement area,damaged tissue analysis and carbonized tissue analysis in the experimental study.The microwave machine and special gas-cooled microwave ablation probes were designed and produced.The microwave machine can output 2450 MHz microwave signal,and its output power can be freely adjustable from 0 to 100 W.The microwave ablation probe has a good air tightness,while the internal antenna surface was welded by special micro thermocouples to help achieve the internal temperature monitoring measurement.The experiments of ablation of porcine liver were carried out under the conditions of no cooling,2MPa,3MPa and 4MPa nitrogen gas pressure respectively.The results of temperature analysis show that the maximum temperature drop is 70.3% and the antenna temperature is controlled at the damaged temperature.The analysis of the damaged tissue shows that the air cooling does not reduce the ablation size and the carbonization of the tissue is improved.The simulation results are validated and supplemented,and the effect of air cooling on the thermal field of microwave ablation is confirmed.