## 4 Conclusions  
The infrared temperature measurement system was set up to measure the temperature elevation of a bovine liver at different power. The temperature rise curves at the focus fall into three broad categories. 1. At a power of 125 W (I \(\approx\) 10,000 W/cm\({}^{2}\)), the tissue temperature at focus rose rapidly to the maximum temperature (>90 \({}^{\circ}\)C) within tens of milliseconds and then fluctuated slightly. 2. When the power was reduced to 40 W (I \(\approx\) 3000 W/cm\({}^{2}\)), the temperature rose rapidly in a short time, reached the maximum temperature of about 77 \({}^{\circ}\)C within 1 s, and was almost kept unchanged. The temperature rise rate of the tissue was still more than 30 \({}^{\circ}\)C/s. 3. When the power was in the range of 4 W to 8 W (MIFU, 240 \(\leq\) I \(\leq\) 500 W/cm\({}^{2}\)), the temperature increased steadily. At the end of sonication, the measured temperature was controlled below 60 \({}^{\circ}\)C.  
Figure 7: The temperature (predicted) of the bovine liver at 40 s at different power. The blue solid line presents the temperature at focus when ignoring blood perfusion (\(w_{b}\) = 0, at focus), the blue dotted line presents the temperature at 1.5 mm away from the focus when ignoring blood perfusion (\(w_{b}\) = 0, 1.5 mm away), the red solid line presents the temperature at focus when considering blood perfusion (\(w_{b}\) = 0.008, at focus), and the red dotted line presents the temperature at 1.5 mm away from the focus when considering blood perfusion (\(w_{b}\) = 0.008, 1.5 mm away). When the blood perfusion was ignored, for a 1 W increase in power, the temperature at focus increased by 3.3 \({}^{\circ}\)C after sonication, and the temperature at 1.5 mm away from the focus increased by 2.5 \({}^{\circ}\)C. When the blood perfusion was considered (\(w_{b}\) = 0.008), the temperature at focus increased by 3 \({}^{\circ}\)C after sonication, and the temperature at 1.5 mm away from the focus increased by 2.1 \({}^{\circ}\)C. With the increase in power, the temperature difference between the focus and at 1.5 mm from the focus gradually increased, and the effect of blood perfusion on the temperature gradually increased. Accurate prediction before operation and optimal control during treatment are the keys to achieving therapeutic effects and avoiding adverse effects when focused ultrasound is applied in tumor ablation. The development of acoustic cavitation, boiling, and shielding of large bubbles and their effects on temperature has not been accurately evaluated and is not included in the classical numerical simulation model. Therefore, it might not be reliable to predict the temperature when the intensity of 1000 W/cm\({}^{2}\) was applied to the tissue; high temperature would lead to tissue boiling and bubble formation and might induce more undefined and less predictable necrosis. These would challenge the effective temperature control during the treatment [27]. For focused ultrasound (MIFU) with an intensity below 1000 W/cm\({}^{2}\), the intensity range was below the cavitation threshold and the temperature increase mainly depended on the thermal effect, and it was easy to assess and predict temperature during treatment. The goal of this study was to control tissue temperature rise until reaching the threshold for thermal necrosis (55 \({}^{\circ}\)C), which could more safely achieve the palliative treatment of tumors. Therefore, this study focused on the intensity range of moderate-intensity focused ultrasound (100 W/cm\({}^{2}\)\(\leq\) I \(\leq\) 1000 W/cm\({}^{2}\)), and discussed the temperature rise at different power in a bovine liver. The simulated and measured results showed that (1) the temperature of the tissue induced by the MIFU at the end of sonication was linearly related to the power and (2) the effect of blood perfusion on temperature increased with the power increase. [PERSON] et al.