# Simulation Study of Microwave Ablation of Porous Lung Tissue
## 1 Introduction  
Cancer is considered to be one of the leading causes of death, hindering the possibility of a global increase in life expectancy [1]. Lung cancer is a malignant tumor with the highest morbidity and mortality rate in the world, which seriously threatens the life and health of human beings [2]. At present, microwave ablation is widely used as an emerging treatment method for parenchymal tumors of the liver, kidney, lung, thyroid, etc., which has the advantages of less trauma, precise positioning, and rapid and efficient inactivation of tumor cells compared with surgery and chemotherapy [3, 4]. The principle of microwave ablation is to insert the microwave antenna into the tumor under the guidance of CT or MRI [5]. The microwave antenna focuses the microwave energy on the tumor, and the tumor tissue will reach a high temperature of 60 \({}^{\circ}\)C-150 \({}^{\circ}\)C in a short time, enabling a complete necrosis to achieve the goal of treatment of tumors [6, 7]. The key to microwave ablation is to destroy the tumor tissue while minimizing the damage caused to the surrounding healthy tissues. More importantly, tumor and normal tissue properties differ greatly, which may have an impact on therapeutic ablation. In this case, a biological heat transfer model close to the clinical effect was constructed for microwave ablation to evaluate the influence of tumor and normal tissue heterogeneity on the efficacy and analyze the temperature distribution and thermal injury volume. It is very important to predict the final ablationarea and volume according to the tumor size, which is beneficial to the accurate treatment of microwave ablation of lung tumors. For this reason, various biological heat transfer models have been developed over the years, starting with the Pennes equation. Pennes biological heat transfer equation is the simplest biological heat equation and is widely used for modeling heat transfer in biological tissues during thermotherapy [8]. However, the Pennes heat transfer equation has the disadvantage of neglecting the direction of blood flow and the reverse flow arrangement of the arteries and veins. This equation assumes thermal equilibrium between venous blood and tissue and assumes a constant arterial temperature of 37 \({}^{\circ}\)C [9; 10]. This is unrealistic in thermal ablation. Biological tissues are complex structures composed of cells of different sizes and microvascular beds. According to the porous medium theory, it can be divided into different phases coexisting in the same domain, namely the \"tissue phase\" and the \"blood phase\". The former consists of cells and intercellular spaces, while the latter represents the vasculature that permeates the entire tissue [11; 12]. During microwave ablation, the more blood vessels there are, the more heat is carried away by blood flow [13]. Therefore, the higher the degree of vascularization of biological tissues, the more it is necessary to use them as porous media in the model, for example, for the liver and lung [14]. At the same time, the heat transfer model using a porous media theory is established with fewer assumptions, so the porous theory is gradually applied to the biological heat transfer model, and a porous media heat transfer model is established. [PERSON] et al. [15] used the eigenvalue technique to study the effects of weak, normal, and strong thermal conductivity on displacement, temperature, stress, and volume fraction fields in two-dimensional porous media. [PERSON] et al. [16] established a theoretical model of porous media in an intermittent microwave heating process and considered the changes in electromagnetic energy, phase transition, and large deformation. [PERSON] et al. [17] developed the porous liver model, including a solid tumor, based on the porous medium model and the generalized two-phase lag (DPL) model. [PERSON] et al. [18] analyzed the thermoelastic response of skin tissue during laser irradiation.