A Gradient Waveform Generator With Self-Trigger Function Used In MRI

Magnetic Resonance Imaging is one of the important research fields of NMR. Nowadays, with the rapid development of the hardware technology in MRI system, it has become more and more important in the clinical diagnostic and scientific researches. The spectrometer is one of the key components in the MRI system, and the gradient waveform generator is one of the important units in the spectrometer. The design of the gradient waveform generator is studied in this thesis in detail, and a method to eliminate the gradient timing jitter is proposed.The main contents of the thesis include:First, the basic principle of MRI is introduced in part 1. It includes the basic principle of the NMR, and the conception of special encoding, K space etc. Besides, some commonly used pulse sequences are also discussed briefly.In the second part, the structure of a typical MRI spectrometer is introduced, it includes the RF transmitter, the gradient waveform generator, the receiver and the pulse sequence generator, the function and the theory of which are introduced briefly.In the third part, a design of a gradient waveform generator with self-triggering function used in MRI is discussed. In the present design, a high precision DAC (24-bit) is used. With the self-triggering function, the gradient waveform generator can work independent of Pulse board. As a result, the problem of group delays arising from the high precision DAC is overcome easily.Finally, a method was proposed to eliminate the timing jitter in the digital gradient waveform generator in the MRI systems, which involves the use of the internal clock of the digital to analog converter (DAC) to synchronize the start of pulse sequence generator. The principle of the proposed method was discussed in detail.