# Computer Simulations of Dual-Antenna Microwave Ablation and Comparison to Experimental Measurements
## 3 Results
### Influences of Heating Parameters on MWA Coagulation Zone  
A dual-antenna MWA coagulation zone is formed by the fusion of two single-antenna coagulation zones. The clinically common heating parameters such as matrix input power  
Figure 5: The results of the 54 \({}^{\circ}\)C, 60 \({}^{\circ}\)C, and 65 \({}^{\circ}\)C isothermal surface and Arrhenius model after 8 min of treatment time.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Spacing**} & **Characteristic** & **Experiment** & **IS-54** & **Arrhenius** & \multirow{2}{*}{**Error-2 \({}^{**}\)**} \\  & **Length** & **Data** & **Model** & **Model** & & \\ \hline \multirow{3}{*}{40 mm} & \(R_{\text{max}}\) (mm) & 69.9 & 74.00 & 66.00 & 5.87\% & \(-\)5.58\% \\  & \(R_{\text{f}}\) (mm) & 20.10 & 21.00 & N/A & 4.48\% & N/A \\  & \(R_{\text{L}}\) (mm) & 42.5 & 44.00 & 35.1 & 3.53\% & \(-\)17.41\% \\ \hline \multirow{3}{*}{30 mm} & \(R_{\text{max}}\) (mm) & 57.88 & 62.00 & 55.00 & 7.12\% & \(-\)4.98\% \\  & \(R_{\text{f}}\) (mm) & 37.75 & 40.00 & 24.00 & 5.96\% & \(-\)36.42\% \\  & \(R_{\text{L}}\) (mm) & 42.63 & 45.00 & 37.00 & 5.56\% & \(-\)13.21\% \\ \hline \multirow{3}{*}{20 mm} & \(R_{\text{max}}\) (mm) & 53.13 & 55.00 & 44.00 & 3.52\% & \(-\)17.18\% \\  & \(R_{\text{f}}\) (mm) & 46.25 & 48.00 & 37.00 & 3.78\% & \(-\)20.00\% \\ \cline{1-1}  & \(R_{\text{L}}\) (mm) & 47.13 & 48.00 & 37.00 & 1.85\% & \(-\)21.49\% \\ \hline \hline \end{tabular}  
* Error-1 indicates the relative errors between the experimental data and IS-54, ** Error-2 indicates the relative errors between the experiment data and Arrhenius model.  
\end{table}
Table 3: Comparisons of experimental data and simulation results under three dual-antenna spacings (in millimeters).  
and different dual-antenna spacings were employed to simulate the changes in the coagulation zone after 8 min of MWA. Table 4 lists the time at which the coagulation zones formed by the two antennas began to fuse under the different heating parameters. It is clear that under the same spacing, the increase in total input power could reduce the time at which the coagulation zone starts to fuse. With regard to the 20 mm spacing and 60 W input power, the fusion of the two coagulation zones occurred at 28 s. For the 40 mm spacing and 60 W input power, it took at least 190 s for fusion to occur. The fusion of two coagulation zones was substantially attributable to microwave energy deposition and tissue heat conduction. As the spacing increased, the interacted microwave energy deposition effects of dual-antennas diminished. This is why the coagulation zone in the case of the 40 mm spacing fused together later. The study of the coagulation zone fusion is helpful for physicians to determine the shortest ablation time for the dual-antenna MWA procedure.  
Based on the dual-antenna FEM model, the effects of different spacing between two applicators and total matrix input powers on the coagulation zone were analyzed. At each spacing (20 mm, 30 mm, and 40 mm), the experiments were conducted with 40 W, 50 W, and 60 W power for 8 min, respectively. It was found that the fusion coagulation zone exhibited specific characteristics at different spacings. For the 20 mm spacing, the coagulation zones of the two antennas fused earliest. As compared to the 30 mm and 40 mm spacings, the depression in the fused coagulation zone between the two antennas was less obvious. With increasing spacing or decreasing total input power, the coagulation zones fused later. The depression in the fused coagulation zone became more pronounced.