High Accuracy Generation Of Pre-emphasised Gradient Signals In Magnetic Resonance Imaging Spectrometer

The spectrometer is an important part of the magnetic resonance imaging system.The gradient generation module has an important influence on the final imaging quality.When the gradient waveform emitted by the spectrometer changes during the imaging process,eddy currents will be generated on the surrounding metal surface,thereby affecting the actual gradient field.At the same time,the change of the gradient field will also generate eddy current which will influence the static magnetic field.These vortices form artifacts and distortions in the final reconstructed image,severely affecting the imaging results and affecting subsequent image analysis.In order to reduce the effect of eddy current effect,a gradient pre-emphasis method based on FPGA(Field Programmable Gate Array)was designed for spectrometer development to compensate the gradient attenuation caused by eddy currents.Using the abundant resources of FPGA and high degree of parallelism,the implementation of the algorithm can be implemented in a three-stage pipeline to achieve real-time requirements of 1μs.This paper not only considers the eddy currents generated by the gradient magnetic field in its own direction,but also takes the effects of the eddy currents of the cross magnetic field and eddy current compensation of the static magnetic field into consideration.This design can provide a flexible and comprehensive solution for eddy current compensation of the gradient field,contributing to the improvement of imaging quality.In the design of spectrometer,uses a digital signal processor(DSP)to control the generating the gradient waveform,DSP compensate parameters and other data to FPGA,and trigger the occurrence of gradient waveforms.Using oscilloscope to observe the rusults,the gradient output results were verified repeatedly.Experiments show that the pre-emphasis method in this project can satisfy the multi-parameter compensation operation and can handle the abnormal conditions such as overflow correctly.In order to verify the credibility and accuracy of the gradient pre-compensation results,the data acquisition based on LabVIEW software and high-speed acquisition card was performed in this paper.The pre-compensation results of the magnetic field were collected and stored,and the parameters of the collected data were fitted and analysis.After the parameter analysis,it is verified that the pre-compensation results of the magnetic field have a high degree of matching and stability with the preset parameters.After repeated experiments,the method in this paper can accurately achieve the pre-compensation of eddy currents,and can maintain stability and credibility over a long period of time.