# Simulation Study of Microwave Ablation of Porous Lung Tissue
## 4 Discussion  
In order to ensure that the tumor tissue is completely destroyed and to minimize the damage to the surrounding healthy tissues, a model that more closely fits the actual lung tissue is needed. [PERSON] biological heat transfer equation does not take into account the porous characteristics of lung tissue and ignores the influence of blood flow [9]. The difference between the lung tissue temperature obtained using the Pennes heat transfer equation and the temperature achieved in the actual ablation in the simulation is large, which will have a certain impact on the ablation efficacy. Therefore, it is important to establish a heat transfer model based on porous lung tissue in microwave ablation. In this paper, a biological heat transfer model based on porous lung tissue was established, and microwave ablation of lung tissue containing tumor tissue was simulated using the finite element method. The effects of tumor diameter, tumor porosity, and microwave ablation power on the ablation effect of porous lung tissue were investigated in terms of tissue temperature distribution, ablation zone, and ablation volume. The results showed that as the tumor diameter increased, the tissue temperature and the longitudinal diameter of the ablation zone decreased, while the ablation volume did not change significantly. The greater the porosity of tumor tissue, the lower the tissue temperature, and the lower the ablation area and ablation volume. The tissue temperature, ablation area, and ablation volume will increase with the increase of ablation power. Therefore, increasing the ablation power can ensure a certain degree of complete ablation of the tumor. The larger the diameter of the tumor, the more abundant the blood vessels deep inside it, the more heat is taken away by the blood flow in the vessels, and the temperature reached by the tumor tissue is subsequently reduced. Since the coaxial single-slot antenna mainly transfers energy along the direction of antenna insertion, it is not conducive to the ablation of large-size tumors in the lateral direction, and the transverse diameter of the ablation zone is consequently reduced, so the treatment difficulty increases. [PERSON] et al. [29] showed that in smaller tumors, the cell death process occurs faster; the percentage of dead cancer cells also decreases by 20% when the tumor diameter increases, and the treatment of large tumors are more difficult than that of small tumors, in agreement with the findings of our study. One of the most important properties of biological porous tissue is the blood volume fraction, i.e., porosity; the greater the tumor porosity, the more blood vessels in the tissue, the more heat is taken away by blood flow, and the lower the temperature reached by the tissue, which further affects the size of the ablation zone and ablation volume. [PERSON] et al. [25] showed that the tissue temperature and ablation zone were much lower at a tumor porosity of 0.23 than at a porosity of 0.07, which also indicates that tumor porosity affects ablation efficacy. In our study, when the ablation power was increased from 10 W to 30 W, the maximum temperature reached by the tissue increased from 87.3 \({}^{\circ}\)C to 142.0 \({}^{\circ}\)C, and the ablation volume increased from 2.28 cm\({}^{3}\) to 4.06 cm\({}^{3}\), and the possibility of complete ablation of the tumor increased, so we believe that the risk of tumor recurrence can be reduced to some extent by appropriately increasing the ablation power. Meanwhile, the porosity changes from the central to the marginal regions of the tumor [29]. However, in the present study, we considered the tumor tissue porosity as a constant value to simplify the study, which is one of the limitations of our study. Also, the variation of electrical properties as well as thermal properties of lung and tumor tissues with temperature was not considered in the numerical simulation.