The Digitalization Of Nuclear Magnetic Resonance System

Nuclear Magnetic Resonance (NMR) technique has become one of the most important tools for probing the material structure, and has been widely used in the fields of substance analysis and medical imaging. Simultaneously, the development of the application field and scientific research in NMR has put high demands on its system technology research. To solve the problems existing in standard commercial spectrometers, we focus our research on the digital investigation of NMR system. This research can optimize the structure and reduce the cost of the system without performance lost. We believe it laid a foundation for the popularization of NMR spectrometers.The main contents in this dissertation are as follows:1. The trend in the digitalization of NMR system. To begin with, we provided an overview of the development of NMR technique. Then we dwelt on the significance of the research work.2. The digital investigation of integrated NMR spectrometer based on USB interface. Firstly, the structure of standard commercial spectrometers was introduced. Then, a complete digital integrated NMR spectrometer was designed. The spectrometer, in which the control/communication unit, pulse generator, RF waveform transmitter and digital receiver are integrated on one PCB card, can works in two modes. Its hardware structure is independent of PC and greatly simplified without the loss of flexibility and performance.3. The digital investigation of F_TDM receiver for parallel acquisition of MRI. In recent years, the rapid development of parallel acquisition in magnetic resonance imaging (MRI) has put high demands on receiver technology. Firstly, the disadvantages of the existing technology were pointed out. Then, an alternative technique F_TDM, which minimizes physical dimensions and system complexity, was proposed and the principle of this technique was discussed. Finally, a PCI-based four-channel F_TDM receiver was designed for verifying and demonstrating the scheme and the performance of this proposed technique.4. The investigation of selective-excitation radiofrequency (RF) pulse for MRI. A selective-excitation RF pulse that uses hard pulses composed of a sequence of composite pulses with positive and negative phases (P/N pulse) was proposed herein. It can be used for imaging studies to improve the efficiency of amplification at the lowest cost. Fourier series have been first used to analyze the equivalence between the proposed P/N pulse and the conventional soft pulse on selective excitation. Subsequently, computer simulations based on density-matrix theory were used to compare the excitation profiles of both the soft and the P/N pulses. In addition, the excitation profiles of the P/N pulses have been measured experimentally and several slices of images have been obtained as proofs by using the multislice SE2D sequence through replacement of the conventional soft pulse by the proposed P/N pulse.5. The summary and prospect of the digitalization of NMR system. We analyzed the existing problems in present works and pointed out the future research direction.