Design Of Radiofrequency Ablation System Based On Single Chip Microcomputer

Radiofrequency ablation(RF)is under the guidance of ultrasound or CT and other visualization of medical equipment that the doctor use the single needle or multi-needle puncture into the human tumor,and then place a larger body surface electrode as the circuit negative on the other side of the disease sites.When the RF current go through the electrode needle into the tumor,there will two parts of the heat,including the Joule heat caused by conduction current and the dielectric loss heat caused by displacement current.Compared with normal tissue,tumor cells are more sensitive to heat.When the temperature reaches a certain degree,the cells coagulation necrosis occurred,so as to achieve the purpose of killing cancer cells.At present,for the treatment of solid tumors,the stable signal source and temperature control system of the radiofrequency ablation instrument are the key points and difficulties in the design of the system.Based on the demand,some modules of the radiofrequency ablation system are designed,including the power adjustable signal generating module,temperature measurement module,temperature control module and system overall control strategy.The details are as follows.(1)The signal generation module was designed based on the direct digital frequency synthesizer DDS(Direct Digital Synthesizer)of chip AD9834 signal control circuit,using AD5660 signal amplitude to control the output power.Then the filter circuit was designed and tested,using MATLAB for spectrum analysis.The results showed that the sine wave frequency concentrated in the vicinity of 460 KHz and the signal was stable.It meets the expected parameters.(2)The temperature measurement module used a dual temperature measurement and control scheme for measuring the center and boundary temperature of ablation tissue.It was designed and tested by the STM32,and error was controlled within 1 degree,in line with parameter requirements(3)In the thermostat design,the temperature control module was designed based on MATLAB Simulink platform,parameterized and compared with PID controller,fuzzy controller and fuzzy PID controller.Through a series of comparative analysis,it was found that the adjustment time of fuzzy PID thermostat is 1.1635 s,obviously better than the fuzzy control of the steady-state error(The adjustment time was infinity NaN because the specified value was not reached).So the fuzzy controller is not considered.Meanwhile,it was also better than the 1.2204 s of PID.The overshoot was an important evaluation parameter of the system stability.The fuzzy overshoot of PID was 0.0455,although it is inferior to the fuzzy controller which was 0,but it was better than the PID controller with 0.8055.As a general view,the fuzzy PID controller was obviously superior to the PID and the fuzzy controller.Simultaneously,the fuzzy PID controller can realize the on-line self-tuning of the parameters,and can meet the dynamic requirements of the system in real time.Therefore,the fuzzy PID was confirmed as the final system.(4)The system temperature control strategy was designed as well.The temperature control real-timely monitored the boundary and central temperature of the ablation.According to the two temperatures,a priority was determined to the heating method.The heating process was divided into two parts,the heating time was about 2 minutes by full-scale heating.Until the boundary area temperature reached 60℃,the ablation system switch to parameter self-tuning fuzzy PID,which made the system stabilized at about 65℃ for ablation.During the whole heating process,the center and boundary temperature of the ablation area were always monitored in real time.If one of the temperatures was higher than the original threshold,the system was automatically cut off and the heating was stopped.This study shows that the core of the DDS signal source can realize accurate amplitude control,and ultimately achieving the purpose of controlling the output power.In the aspect of temperature measurement and control,two thermocouples were used to measure the center and boundary temperature of the ablation,monitoring in real time.Finally,the RF heating power was adjusted by parameter self-tuning fuzzy PID controller so as to achieve the purpose of rapid and effective ablation.