【正文】 cessary after each step to manually change the input file for ABAQUS and apply a new input voltage and set the step size. In this case the operator would have to check the results file after each step (. in 6 to 11 min intervals), modify the input file and restart ABAQUS. Results and Discussion Fig. 4 shows the resulting tip temperature and the applied voltage for the first 200 s of the closed loop system consisting of the FEM model and the control software. No results are shown after 200 s since there was little change once the set tip temperature was reached. Fig. 4 also shows the results of the control system simulation. There is good correlation between the control simulation and the closed loop system consisting of the FEM model and the control software. We explain deviations between the two by inaccuracies of the approximation (see (2)) and differences in step sizes. In the control system simulation a constant sampling time (. step time) of 10 s was used. However, the algorithm implemented in the control program did not use constant step times. Step time was increased if the change in tip temperature between the steps was below a certain value. Note that the parameters of the controller must be modified when boundary conditions (. perfusion), electrode 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。103 1/s [15]. An input file was submitted to ABAQUS, in which geometry, material properties, step time and boundary conditions were specified. The applied voltage was one of the boundary conditions and remained constant during each step. ABAQUS created a results file in which temperatures of all nodes of the FEM model at the end of the step were written. We created a C++ program that reads the temperature at the electrode tip from the results file and creates a new input file where the applied voltage is set according to a control algorithm。C cell necrosis occurs after ~3 min [12]. A monly used mode is temperaturecontrolled ablation, where the tip temperature of the electrodes is kept at a predetermined value, usually around 100176。C. The closed loop system simulation output closely correlated with the FEM model, and allowed us to optimize control parameters. Discussion The closed loop control of the FEM model allowed us to implement temperature controlled RF ablation with minimal user input. Keywords: ablation。此前 ,研究人員經(jīng)常應(yīng)用恒功率 ,或使用耗時的試錯方法來確定所需電壓。 在肝射頻消融 ,消融次臨床用于上升到 35分鐘。獲得相同的性能在初始階段在這兩種情況下 ,不同的控制器必須被使用 ,如 PI控制器的參數(shù)進(jìn)行了修正。然而 ,該算法實(shí)現(xiàn)控制程序沒有使用固定步長時期。不使用控制程序、手動交互是8 必要的在每一步后手動更改輸入文件進(jìn)行有限元分析 ,并應(yīng)用一個新的輸入電壓和設(shè)置步長。 這個計劃被重復(fù) ,直到消融被模擬為所需的時間。一個輸入文件被創(chuàng)建和 ABAQUS有限元分析解決了有限元模型。超調(diào)量為 11%,148年代后達(dá)成。 我們模擬閉環(huán)系統(tǒng)的行為與軟件安裝在豬體內(nèi)的實(shí)驗與麗塔 500發(fā)電機(jī)和模型 30我們認(rèn)為電極需要 1到 2分鐘的提示溫度達(dá)到目標(biāo)溫度 100176。我們選擇了相對簡單的 PI控制器對我們控制系統(tǒng)。這個軟件允許我們近似系統(tǒng)從其階躍響應(yīng)通過遞歸最小平方算法 ,給出了參數(shù) a0、 a a b1和 b2的 (2)。在實(shí)現(xiàn)控制器 ,我們分析了動態(tài)系統(tǒng) (即有限元模型 )來控制。 一個輸入文件被提交到有限元分析中 ,幾何、材料性質(zhì)、邊界條件的步驟的時間和指定的。 C(熱邊界條件 )和 0 V(電邊界條件 )。方程 (1)定義解決方案在空間域包括電極和組織。 3 方法 有限元方法 射頻消融破壞組織的熱能量 ,轉(zhuǎn)化為電能。 圖 圖 30傘探針用于有限元模型的尖頭叉子和遠(yuǎn)端 10毫米的軸進(jìn)行射頻電流。組織損傷可以發(fā)生在溫度高于 43176。有限元方法 背景 射頻 (RF)消融已成為相當(dāng)重要的作為一個微創(chuàng)治療原發(fā)性和轉(zhuǎn)