# Computer Simulations of Dual-Antenna Microwave Ablation and Comparison to Experimental Measurements
## 4 Discussion  
MWA for liver tumors is becoming increasingly popular because of its broad indications, ease of operation, and rapid recovery. In order to achieve the treatment of larger tumors, dual-antenna or multi-antenna ablations have been employed. However, most MWA treatment planning schemes [41; 42] are based on single-antenna simulations. The multi-antenna coagulation zone was simply considered as a superposition of different antenna MWAs, thus lacking a complete numerical analysis. The simulation accuracy of dual-antenna or multi-antenna ablations needs to be further improved. [PERSON] et al. [43] studied ablation zones created by double-slot coaxial antennas in triangular and square configurations. However, their theoretical parametric study did not take parallel dual-antenna MWA into account. [PERSON] et al. [44] found that the dual-slot microwave antenna can create a more spherical ablation zone than the monopole antenna. The direct spacing of the two transmitting points of the dual-slot antenna was fixed. How the heating parameters (total input power, antenna spacings, etc.) affect the coagulation zone is still unknown. Therefore, the current work aimed to study the temperature distribution and the coagulation zone changes under different heating parameters by using two monopole antennas. A dual-antenna FEM model was developed to show the temperature distribution and the coagulation zone over time. [PERSON] and [PERSON] [33] mentioned the use of the Arrhenius method to characterize the coagulation zone. This study was based on the results of single-antenna multi-slot coaxial MWA. In addition, the isothermal method was used to characterize the coagulation zone. In some previous studies, the dual-antenna (multi-antenna) MWA coagulation zone was characterized by the superimposition of single-antenna coagulation zones. In our FEM simulations, the IS-54 surface was used to characterize the coagulation zone because this model was more consistent with the ex vivo experiment results. Figure 6: Temperature rising curves at point P1 under three different blood perfusions (dual-antenna spacing: 30 mm; heating parameter: 50 W matrix input power, and 8 min treatment time). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Blood Perfusion \(\omega_{\text{b}}\) (kg/(m\({}^{2}\cdot\)s))**} & **1.0** & **1.5** & **3.0** \\ \hline
**Antenna Matrix Spacing, Total Input Power** & 18.1\% & 25.2\% & 41.9\% \\
2 cm, 50 W & 17.3\% & 24.4\% & 40.6\% \\
2 cm, 60 W & 16.9\% & 23.8\% & 39.8\% \\
3 cm, 40 W & 18.4\% & 25.9\% & 43.0\% \\
3 cm, 50 W & 17.6\% & 24.6\% & 41.5\% \\
3 cm, 60 W & 17.0\% & 23.8\% & 40.1\% \\
4 cm, 40 W & 20.2\% & 28.7\% & 48.0\% \\
4 cm, 50 W & 19.1\% & 26.8\% & 45.2\% \\
4 cm, 60 W & 18.1\% & 25.6\% & 43.4\% \\ Mean & 18.4\% & 25.4\% & 42.5\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Reduction in coagulation zone volume under three types of blood perfusion. The SAR coefficient plays an important role in the MWA temperature distribution simulation. Furthermore, SAR is directly related to the electric field strength affecting the tissue (see Equation (2)). Thus, this study discussed the electric field changes along the axis \(y=0\) (Figure 2) for single-antenna MWA and dual-antenna MWA. Figure 7 illustrates the diagram of single-antenna electric field distribution at 480 s. The electric field intensity on both sides of the antenna is substantially symmetrical. In the case of dual-antenna MWA, the trends of the temperature changes and the electric field are essentially the same (Figure 8). The dual-antenna electric field intensity at the respective point is not a linear superposition of two single-antenna electric fields, but rather less than the sum of both single-antenna electric field intensities. This is due to the fact that at respective timepoints, the temperature in dual-antenna MWA is higher than the corresponding temperature in single-antenna MWA, leading to the declines in the electric parameters being more rapid in dual-antenna MWA.