Studies Related To Magnetic Resonance Imaging (MRI) System

With rapid development of technology and application of magnetic resonance imaging (MRI), MRI system must meet higher performance requirements. This paper focuses on two aspects, those are the quality of MRI and universal application of digital frequency source, to further enhance the performance of MRI system.Uniformity and stability of the main magnetic field Bo, as well as the linearity of the field gradients, play a crucial role in the quality of MRI. In order to obtain better MRI images, we can track changes of magnetic field intensity and collect the real-time data of magnetic field. The data can be used to lock magnetic field of the MRI system and correct the signal in the process of data post-processing. Thus, a magnetic resonance-compatible monitoring system based on19F-NMR is developed to monitor changes of the magnetic field intensity for the late correction of MRI images and magnetic field locking.Meanwhile, with higher requirements for MRI experiments, more and more complicated MRI sequences were developed, such as rapid imaging sequence and multi-layer imaging sequence, MRI digital frequency source is required to support a larger amount of waveform data, a shorter time of data transmission from PC to board in TR and a faster update rate. A digital frequency source with high performance is developed in this thesis.The main contents of this thesis are as follows:1. A magnetic field monitoring system for MRI system based on19F-NMR. First, this thesis shows that uniformity and stability of the main magnetic field Bo, as well as the linearity of the field gradients, are crucial factors that will affect the image quality of MRI. And then, the architecture and the development process of magnetic field monitoring system are described in detail, including probe development and system integration. Finally, the performance of the magnetic field monitoring system is demonstrated in a home-built0.3T MRI system.2. MRI digital frequency source. First, this paper gives a brief introduction of the original digital frequency source, including the principle and architecture, as well as limitations in complex MRI application. And then, the design process of higher-performance digital frequency source is described in detail. Wave concepts and run-length encoding(RLE) are proposed to optimize the data storage mode and shorter the time of data transmission from PC to board in TR, and the burst read mode of SDRAM and the system clock multiplication of FPGA are proposed to improve the update rate. Finally, the debugging test of the digital frequency source is mainly described.3. Summary and Prospect. We summarize the research work and existing problems, and put forward the new opinion of the study in future.