| Lung cancer is the most common malignant tumor in the world.It is a serious threat to human health.Microwave ablation(MWA),as a local minimally invasive treatment technology,has an efficient killing effect on primary and metastatic lung cancer.The principle of MWA is to use image technology to guide microwave ablation antenna to puncture into the lung tumor through the skin,release microwave electromagnetic energy,make the polar molecules in the tumor tissue vibrate at high speed,and produce a high temperature of 65-150°C in a short time,coagulative necrosis of tumor tissue(protein denaturation temperature 60°C or above)to achieve the purpose of tumor treatment.However,in the current clinical application of microwave ablation in the treatment of lung cancer,the treatment effect will be affected by the air in the lung.The microwave energy is accumulated in the lung tissue and is not easy to transfer,which makes it very difficult to accurately predict and control the ablation area.In the treatment of some large tumors and irregular tumors,the ablation area may not completely cover the focus and the tumor may recur after operation;Or cause excessive ablation and damage to healthy tissues.This subject carries out numerical simulation and in vitro experiment on the microwave ablation heat field of inflated lung tissue,and obtains the distribution law and basic data of microwave ablation heat field of inflated lung,in order to solve the problem of accurately controlling the ablation heat field and further improve the safety and effectiveness of microwave ablation.The specific research contents include:(1)Use COMSOL Multiphysics multiphysics coupling software to build an idealized geometric model of microwave ablation antenna and lung tissue,set the inflatable group(inflated lung tissue)and the control group(completely deflated lung tissue)according to different material properties.The electromagnetic field and biological heat transfer are coupled to solve and calculate the change law of microwave ablation thermal field of inflatable lung tissue under different ablation powers(40W,50 W,60W)and ablation time(100s,200 s,300s),to explore the effect of lung tissue on microwave ablation under inflated state.(2)Use a 2450 MHz frequency microwave ablation instrument,an air compressor,and a thermocouple temperature probe to build an in vitro ablation experimental platform to conduct ablation experiments on in vitro air-filled pig lungs to obtain the thermal field distribution and basic data under different ablation parameters to verify The accuracy of numerical simulation results.(3)The open coaxial probe method was used to measure the dielectric properties of isolated porcine lung tissue at different temperatures(25-100 °C)to simulate the changes in the dielectric properties of the lung tissue during the actual ablation process.The measured change law of the relative permittivity of lung tissue was fitted into a mathematical model by MATLAB software,and imported into COMSOL Multiphysics software as a dynamic parameter to optimize and compare the original simulation model to obtain more accurate numerical simulation results.The numerical simulation results show that:(1)Under the same combination of ablation parameters,the long diameter,short diameter and maximum temperature of the ablation area of the inflated lung were smaller than those of the control group.Within 300 s of the ablation time,when the ablation power was 40 W,50 W,and 60 W,the long diameter of the ablation area of the inflated lung was 35.0-38.3 mm,40.7-44.2 mm,44.9-48.7 mm;the long diameter of the control group was 36.1-41.1 mm,41.2-45.9 mm,44.9-50.9 mm.The short diameters of the ablation areas of the deflated lung were 18.3-21.4 mm,20.9-24.4 mm,23.2-27.2 mm,respectively;the short diameters of the control group were 22.5-27.4 mm,25.1-30.3 mm,26.8-32.9mm.The highest temperatures in the inflated group were 103.8 °C,121.6 °C,and139.3 °C,respectively;the highest temperatures in the ablation zone in the control group were 124.1 °C,147.0 °C,and 170.0 °C,respectively.(2)The isoperimetric ratio(A measure of the roundness of two-dimensional object,close to 1 is regarded as an ideal perfect circle)of the ablation area of the deflated lung was in the range of 0.75-0.80,while the isoperimetric ratio of the control group was around 0.82-0.86,under the same ablation power and ablation time,the isoperimetric ratio of the control group were higher than the inflated group.In addition,the isoperimetric ratio of the control group decreased with increasing ablation power,while the isoperimetric ratio of the inflated group did not change significantly with the power.The results of in vitro experiments show that:(1)When the ablation power is 40 W,50 W,and 60 W,the average long diameter of the control group are 20.8%-30.9%,7.6%-22.6%,10.4%-19.8% larger than those of the inflated group,respectively.The difference is in the range of 2mm-6mm;the average short diameter of the control group is 24.5%-41.4%,31.6%-45.7%,27.3%-42.9% larger than that of the inflated group,and the difference is about 4mm-10 mm.(2)During the microwave ablation process,the heating rate of the control group at different positions around the antenna was significantly higher than that of the inflated group,and the temperature of the control group was also higher than that of the inflated group throughout the ablation process.(3)The isoperimetric ratio of the ablation area in the inflated group was in the range of 0.81-0.89,and the isoperimetric ratio of the control group was around0.89-0.94.Under the same ablation power and ablation time,the isoperimetric ratio of the ablation area in the control group was larger than the inflated group.In this study,the following conclusions were obtained:(1)Under the same ablation power and ablation time,the long and short diameters of the ablation area of the inflated lung were reduced compared with those of the deflated lung,and the reduction of the short diameter was greater than that of the long diameter.The isoperimetric ratio of the ablation area of the inflated lung is lower than that of the deflated lung,and the shape of the ablation area tends to be slender and oval,which may cause the ablation area to fail to completely cover the tumor,resulting in incomplete ablation or damage to the healthy tissue around the tumor.In clinical treatment,measures such as one-lung ventilation can be considered to reduce pulmonary ventilation.(2)The isoperimetric ratio of the ablation areas of both inflated and deflated lungs tends to increase with the prolongation of ablation time,and the isoperimetric ratio of deflated lungs will decrease with the increase of ablation power,which can be considered in clinical applications.Use the "low power,long time" ablation parameter combination to obtain a more circular ablation area.(3)The relative permittivity of lung tissue will decrease significantly with the increase of temperature.When the fitted mathematical model is used instead of the fixed value as the material property of the simulation model,the experimental results with smaller error from the in vitro experiment are obtained.More accurate simulation results may be obtained if the laws of changes in the dielectric properties and thermophysical parameters of lung tissue with temperature are considered in the numerical simulation experiments.In this study,the thermal field of microwave ablation of inflated lung tissue was simulated and studied in vitro,and the distribution law of microwave ablation thermal field of inflated lung tissue was obtained,which provided basic data and theoretical reference for the clinical application of MWA,and further improved the safety and effectiveness of this operation. |
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