A Gradient Waveform Generator With The Function Of Pre-distortion

Magnetic Resonance Imaging (MRI) can collect vivo information accurately and non-invasively, it is widely used in clinical application and scientific research. The gradient subsystem of MRI scanner is used to produce gradient magnetic field for spatial-encoding. In gradient subsystem, the gradient waveform generator is used to generate gradient waveform, and mostly with the function of pre-emphasis. Pre-emphasis can be divided into analog pre-emphasis and digital pre-emphasis. Analog pre-emphasis is realized by analog circuit and the disadvantage of this method is that the fitting flexibility of pre-emphasis waveform is poor. In digital pre-emphasis, the waveform data are calculated by digital circuit and then converted into analog signal by Digital Analog Converter (DAC), the disadvantage of this method is that it requires DAC with more number of digits, resulting in reduced resolution of the gradient waveform.To solve the above problems, this thesis proposes a gradient waveform generator based on analog pre-emphasis and with the function of pre-distortion. It can add both overshoot and undershoot to the gradient waveform by the use of analog differential circuit in order to improve the fitting flexibility of pre-distortion waveform. With the use of digital potentiometer instead of mechanical potentiometer in this design, the adjustment flexibility and the stability of waveform parameters are improved. In addition, the gradient waveform generator is designed as a PCB based on the Peripheral Component Interconnect (PCI) bus. The PCI address space of the control computer occupied by the gradient waveform generator is reduced by optimizing the internal logic of the gradient waveform generator, facilitating the expansion for multichannel MRI system.