## 4 Discussion
### Damage Volume Comparison  
To clarify damage to muscle, fat, and bone during the thermal ablation process, the damage fraction based on the temperature threshold method was calculated, and a damage cloud map is drawn in Figure 6. The shape of muscle damage could map similar to that of the temperature cloud map. After the heating is stopped, due to temperature hysteresis away from the position of the ablation antenna, thermal damage further expands. The map is convex at the place adjacent to the high-temperature area of the ablation antenna. After the heating is stopped, thermal damage in the high-temperature area is more serious. Because the temperature of fat is low, the contour of the damage cloud map is very close to its temperature cloud map at 60 s. Even during the cooling period, the overall shape does not change much. Similar to muscle, the location of the high-temperature area will still bulge and cause some additional damage. All fat damage is 100% irreversible damage. For bone, the correlation with the temperature cloud map can only be seen in the 15 s damage cloud map. After further heating, the fraction with 100% irreversible damage is close to a cylindrical shape. Although the influence range and temperature of two high-temperature areas in bone are pretty different, their damage effects are more closely related. Damage is the most serious in the area of about z = 10 mm\(\sim\)z = 20 mm. After heating is stopped, the top section of the bone quickly becomes completely necrotic. The lower section is different, and there are still some fractions with no damage. For more accurate analysis, damage cloud map is quantified (Figure 7). For muscle, fat, and bone, three sequence points (z = 10 mm, z = 12 mm, and z = 18 mm) are taken, and damage fraction of all points from 0 to 120 s is plotted. Also, bone damage fraction is additionally calculated at z = 5 mm. Although damage is very different, muscle, fat, and bone still have obvious things in common: damage is mainly concentrated from ablation antenna needle to top of axis, and the lower part of axis is not easily damaged. Even if damage to the upper part of bone spreads in a large area, the lower part can still maintain a good cell survival rate. For muscles, from ablation antenna needle to 18 mm, position is getting closer to its high-temperature region. So, the increase rate of damage fraction and complete damage gradually increased. Two high-temperature regions of fat are at z = 12.0 mm and z = 17.5 mm respectively, resulting in a faster growth rate of damage fraction to 100% near z = 12.0 mm. z = 18.0 mm is very close to another high-temperature region. Its damage rate is relatively slow, but it is higher at a location far from ablation antenna. For bones, position close to ablation antenna is almost completely damaged by heating. As for locations near high-temperature region, higher temperature makes it have stronger thermal diffusion ability, which has some impact on distant locations. It is obvious that growth of complete damage of all positions is very fast at z = 18.0 mm. It can be seen that temperature and damage have obvious boundaries at ablation antenna needle. In addition, high-temperature region at ablation antenna needle is limited compared to other locations. Although high-temperature region near ablation antenna needle is larger than that near groove, temperature and thermal damage of two high-temperature region of bone  
Figure 5: Temperature distribution at the horizontal thermometric sequence of the highest temperature point near ablation antenna. (**a**) Temperature distribution from muscle; (**b**) Temperature distribution from fat; (**c**) Temperature distribution from the bone. and fat are significantly different. Temperature and heat damage near slot are higher than those near needle. Figure 6: Damage fraction cloud map at 15 s, 30 s, 45 s, 60 s, 75 s. Damage fraction is calculated by temperature threshold.