【正文】 geometry etc. are changed. Otherwise there will be changes in the dynamic behavior of the closedloop system. Fig. 5 shows the temperature and voltage of the FEM model controlled by the same PI controller for two cases. The light graphs show the behavior without incorporating perfusion in the FEM model, the dark graphs show the behavior of the same FEM model with perfusion (as in Fig. 4). Both the overshoot and the settling time of tip temperature for the case with perfusion were higher. Also, the voltage required to keep the tip temperature at the set temperature value was higher because the perfusion carried heat away. To obtain the same performance during the initial period in both cases, different controllers had to be used, . the parameters of the PI controller had to be modified. Our model only included a quarter of the actual electrode. In models where nonuniform heating due to vessels occurs, the electrodes will obtain different temperatures [6]. In this case, the temperature of the hottest electrode should be used for control to avoid tissue overheating. 23 Temporal behavior of tip temperature and applied voltage of the closed loop system. The upper curves show the tip temperature, the lower curves show the applied voltage. The light curves show the results of the controlled FEM model without perfusion. The dark curves show the results of the controlled FEM model incorporating perfusion. In hepatic RF ablation, ablation times clinically used go up to 35 min. Since the heatup period is parably much smaller (1 to 2 min.), it is not of essential importance that the temporal behavior of the control algorithm reproduces the control algorithm used in clinical devices during the heatup period. From our experience, the temperature distribution in the FEM model reaches close to steady state at the end of the simulation due to the long simulation times. As long as the tip temperature is kept within a small range around the target temperature after the initial heatup period, the model results (. final temperature distribution) should not differ significantly. However, with knowledge of the actual control parameters and algorithms of mercial devices (. obtained from measurements), accurate simulations of these devices is possible using our methods. Conclusion We implemented a closed loop control system to a FEM model, to automate simulation of temperaturecontrolled RF ablation. We further used a closed loop control system 24 simulation to optimize control parameters. Previously, researchers often applied constant power, or used timeconsuming trialanderror methods to determine required voltage. Furthermore, if control parameters and algorithms of mercial devices are known or can be measured, an accurate simulation of mercial devices is possible. Authors39。 contributions DH carried out puter simulations. 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