## 3 Results
### Ex-Vivo Experiment
#### 3.1.3 Temperature at Different Positions  
The temperature distribution around the microwave antenna is oval. Four temperature sampling points are set perpendicular to the puncture direction of the antenna, which are at the crack of the microwave antenna and 5 mm, 10 mm and 15 mm away from the crack of the antenna. The results are shown in Figure 7.  
The necrotic area formed by microwave ablation is mainly determined by two factors, one is the active heating area formed by the deposition of microwave energy in the tissue, the other is the passive heating area formed by the thermal conduction of tissue due to the existence of temperature difference. The formation of the active heating zone is related to the dielectric properties of the tissue, and the passive heating zone is related to the thermal conductivity of the tissue.  
In the vicinity of the microwave antenna (antenna slot, 5 mm away from the slot), the temperature of the deflated group and the inflated group increased sharply. With the extension of ablation time, the heating rate gradually slowed down and tended to be stable. Under different ablation power (60 W, 50 W, 40 W), the highest temperature at the slot in the deflated group was 103.1 \({}^{\circ}\)C, 101.3 \({}^{\circ}\)C, 88.4 \({}^{\circ}\)C, and the highest temperature at 5 mm away from the slot was 100.0 \({}^{\circ}\)C, 98.1 \({}^{\circ}\)C, 82.6 \({}^{\circ}\)C, respectively; the highest temperature at the slot in the inflatable group was 98.9 \({}^{\circ}\)C, 92.2 \({}^{\circ}\)C, 83.4 \({}^{\circ}\)C, and the highest temperature at 5 mm away from the slot was 95.0 \({}^{\circ}\)C, 86.6 \({}^{\circ}\)C, 75.1 \({}^{\circ}\)C, respectively. In the initial stage of ablation, the heating rate of the deflated group was significantly higher than that of the inflated group, and the temperature of the deflated group was always higher than that of the inflated group during the whole ablation process. The temperature growth of the  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Time/s**} & \multicolumn{2}{c}{**40 W**} & \multicolumn{2}{c}{**50 W**} & \multicolumn{2}{c}{**60 W**} \\ \cline{2-7}  & **Deflated** & **Inflated** & **Deflated** & **Inflated** & **Deflated** & **Inflated** \\ \hline
100 & 0.908 & 0.879 & 0.912 & 0.837 & 0.889 & 0.836 \\ \hline
200 & 0.889 & 0.878 & 0.941 & 0.849 & 0.908 & 0.811 \\ \hline
300 & 0.937 & 0.880 & 0.921 & 0.895 & 0.939 & 0.874 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Isoperimetric ratio of ablation area in each group.  
lung tissue near the antenna mainly depends on the deposition of microwave energy. The relative permittivity and conductivity are the two main factors affecting the deposition of electromagnetic energy, which will significantly increase the temperature of the external heating area [32; 33; 34]. However, the relative permittivity and conductivity of the lung in the inflation state were lower than those in the deflation state, resulting in the temperature of the deflated group was always higher than that of the inflated group.  
At a distance of 10 mm and 15 mm from the antenna, the initial heating rate of the deflated group and the inflated group increased slowly and tended to be linear. During the whole ablation process, the temperature of the deflated group was also higher than that of the inflated group. The ablation area slightly away from the antenna is formed by tissue thermal conductivity, which has a great relationship with the thermal conductivity of the tissue. The thermal conductivity of the inflatable lung is slightly lower than that of the definlatable lung, resulting in the higher temperature of the deflated group than that of the inflated group.