## 3 Results
The temperature also rises with the ablation time, reaching a value  
Figure 5: Results of (**a**) two-dimensional axial-symmetric and (**b**) full three-dimensional simulation models of the temperature (expressed in \({}^{\circ}\)C) distributions in the liver tissue after 600 s of microwave ablation at a frequency 2.45 GHz and the input power of 10 W.  
Figure 6: Isocontours represent the totally ablated regions (gray surfaces) around the liver tumor [70] (triangulated surface) exposed to 600 s of microwave ablation at 2.45 GHz and the three values of the input power (10 W, 13 W, and 15 W). of around 104 \({}^{\circ}\)C after 600 s. As expected, a multislot antenna structure enables more localized near-spherical heating distributions. Isocontours that correspond to the temperatures of 40 \({}^{\circ}\)C (light gray), 60 \({}^{\circ}\)C (light brown), and 70 \({}^{\circ}\)C (brown) around the tumoral tissue (triangulated surface) are plotted in Figure 9a. Close to the antenna the heat source is stronger, so the temperature is higher. The time dependence of the temperatures at four test points (A, B, C, and D) marked in Figure 4b can be seen in Figure 9b. All curves have the same tendencies for all test points. For channel D (located near the heating center), the temperature rapidly increased to approximately 79 \({}^{\circ}\)C after 70 s and then steeply rises up to 105 \({}^{\circ}\)C after 600 s, which is in line with the temperature distributions shown in Figure 8 and the data found in the literature [54]. In contrast, the lowest value of the temperature of around 48 \({}^{\circ}\)C after 600 s is calculated for channel C which is the most distant from the antenna. The maximal temperatures recorded at the points located along the radial direction concerning the maximum transverse of each antenna D (close to the heating center) and B (away from the heating center) differ by around 42%. On the other hand, the maximal value of the temperature at point D is larger by around 37% and 53% than those in points A and C distributed at a distance from the heating center along the antenna shaft, respectively. Figure 8: Temporal evolution of the temperature (in \({}^{\circ}\)C) when an early-stage HCC [70] is treated by microwave ablation at a frequency of 2.45 GHz and input power of 13 W in \(y\)–\(z\) cut plane. The boundary of the tumor tissue is marked by the black line. Figure 7: (**a**) \(x\)–\(y\), (**b**) \(y\)–\(z\), and (**c**) \(x\)–\(z\) cut planes of the total power dissipation density (expressed in W/m\({}^{3}\)) calculated for the liver tumor [70] (plotted as triangulated surface) exposed to microwave frequency of 2.45 GHz and input power of 13 W after 600 s.  
Numerical predictions of the fraction of necrotic tissue during MWA at a frequency of 2.45 GHz and the input power of 13 W are presented in Figure 10. The black line denotes the boundary of the tumoral tissue. Regardless of the time, the damage zones are concentrated around the tip and slots of the antenna, while the backward heating effect is smaller. The use of multiple slots in the antennas provided a more spherical ablation volume for the tissue heated. Thermally ablative devices lead to necrotic tissue with two distinct heating zones, recognized as an active heating zone and a passive heating zone [90]. The active heating zone arises within the tissue nearest to the device where the intensity of energy is high and its absorption by tissue is fast. On the other hand, the passive zone is outside the active zone, far from the ablation device where the intensity of energy is lower. Isocontours related to fractions of damage of 0.3 (violet), 0.5 (blue), 0.75 (dark green), and 1 (dark gray) are shown in Figure 11a. Figure 11b demonstrates the time evolution of the necrotic tissue at four test points (A, B, C, and D) marked in Figure 4b. For test points A, B, and D, at the beginning of the ablation, the tumor damage gradually increases and then reaches a saturation region, which presents the completion time of tumor necrosis.