Research On Components Of Magnetic Resonance Imaging System

Magnetic resonance imaging (MRI) is a tool of non-invasive and non-ironic, which appeared in 1973. MRI has been widely applied to structural and functional imaging, and has become a routine medical imaging technique with X-ray, CT, ultrasonic imaging and PET. In this thesis, frequency source and gradient coils are developed in detail, which are key components in MRI scanner.The main contents of the thesis include:The theory of MRI is introduced briefly, including nuclear magnetic resonance (NMR) and special encoding. The structure of MRI scanner is described, which consists of magnet subsystem, spectrum subsystem and computer subsystem.The design of gradient coils is reviewed. Tow kinds of gradient coils------discrete winding coils and distributed winding coils, are referred. The latter is described in detail, which applies several kinds of optimizations, such as matrix inversion method, target field method, minimum energy, stream function method, and so on. Eddy current must be considered. Traditional reducing eddy current techniques are compared, including anti-eddy-current board, pre-emphasis. current and self-shielded coils. The design of bi-planar mini gradient coil is described in detail.Finally, the complete digital frequency source is introduced. In this part, the direct digital synthesis technique is compared to traditional frequency synthesis techniques. PCI bus technique and PCI interface chip are referred. The structure of the frequency source is described. Results of performance test and application in the integrated MR spectrometer are given.