The Desing And Key Technical Analysis Of Control System Of Mri Gradient Amplifier

Magnetic resonance imaging as a new clinical diagnostic imaging tool, has been widely used, and shows broad prospects for development. However, our level of MRI study is far behind the developed countries, and magnetic resonance imaging equipment has been dependent on foreign imports, to develop a high performance magnetic resonance equipment has an great influence on improving our level of health care. Gradient amplifier as a core component of the MRI system, providing spatial gradient magnetic field orientation and gradient echo generated imaging, its performance directly affects the quality and speed of MRI imaging. With the increasingly high demand for MRI imaging, to design a high performance gradient amplifier is particularly important.Based on the analysis of the needs of gradient amplifier control system, this paper designs a high performance control system with digital control method which is divided into the main control system and monitoring system. This paper designs its hardware circuit and software system. The main contents are as follows:1. This paper studies the function and structure of the gradient amplifier, introduces the main circuit topology of the control system, completes the overall design of the control system according to the needs of gradient amplifier.2. This paper designs a control system hardware circuit, including the AD7656 analog-digital conversion circuit, filter circuit, alarm circuit and monitoring signals sampling circuit. Using TMS320F28335 as the main chip, extends AD7656 to synchronously sample three signals and synchronously control the gradient magnetic field of these three directions. Comparison of the performance of different filters, this paper selects Sallen-Key filter as low-pass filter. Use opto-TP521 to realize enabling and alarm function. Complete the monitoring signals sampling isolation circuit by HCNR200. Finally, this paper completes the above circuit board according to the schematic design, and then conducts a detailed analysis of layout and electromagnetic compatibility.3. On the basis of the hardware circuit, this paper completes the software design of master system and monitoring system for gradient amplifier. Master system uses incremental PID algorithm as the basis of control algorithm. Monitoring system uses ADC module of DSP to sample monitoring signals and completes communication module by MODBUS protocol. In order to reduce the driving current ripple, this paper suggests a novel control method to make the frequency of control and ripple up to twice the frequency of switching, thus can effectively reduce the output current ripple. As the traditional control algorithm does not meet the system requirements, this paper designs an adaptive PID control algorithm to balance its speed and stability.4. After repeated debugging and verification, this paper finally completed the design of gradient amplifier control system, scans signal sequence completely in MRI system and gets water modeling images which meets imaging requirements.