The Digital Spectrometer For Magnetic Resonance Imaging

In recent years, the rapid development of Magnetic Resonance Imaging has raised the new requirements on MRI spectrometers. Commercial spectrometers from many manufacturers, though powerful, are unfavorable in many cases due to its cost. Luckly, these difficulties can be conquered by utilizing the newly developed digital techniques, without scarifying any performance and functionanity. Therefore, in authors' opinions, it is important and valuable to investigate a new generation robust digital MR spectrometer for MRI applications.In this thesis, the digital MR spectrometer techniques were discussed in detail. Moreover, for verification and demonstration popurses, a flexible digital MRI spectrometer with high performance and low cost was built.The main contents of the thesis include,1. The research of digital transmitter in MRI spectrometer. First, the principle and advantage of digital frequency synthesize technique were introduced. Then, a practical digital transmitter was designed. Finally, the output spectrum of the digital transmitter was verified by experimental results.2. The research of digital receiver in MRI spectrometer. In this part, the mechanism of digital quadrature detection technique was analyzed. The design of a complete digital receiver and a direct RF sampling receiver was also presented. Then, unknown acquisition delay problem caused by a digital receiver without external synchronization in MRI was discussed in detail. An effective procedure was suggested for overcoming the problem. The main feature of the proposed method is minimal hardware modifications. The proposed method ensures that most commercial digital receiver can be fully implemented in MRI. In addition, a frequency domain multiplexing technique and a practical four channel FDM receiver were introduced. It is expected that the FDM technique, with the development of commercially available digital receivers, may be valuable and cost-effective in design of parallel MRI receiver system.3. The research of digital pre-emphasis gradient waveform generator. A versatile and inexpensive gradient waveform generator based on the Peripheral Component Interconnect bus of personal computer especially designed for magnetic resonance imaging is presented. Three independent gradient waveform channels on a printed circuit board were accomplished as the sources for x, y and z gradients. The main feature of the present design is...