Communication Module Design And Eddy Current Compensation For A MRI Spectrometer

Magnetic Resonance Imaging (MRI) is an imaging technology which uses the RF pulse and gradient magnetic field to inspire nuclear magnetic resonance signals, and realizes image reconstruction method. Compared with X-ray CT, it has many features such as high resolution, spatial resolution, multi-imaging parameters, arbitrary slice imaging and non-invasive. After rapid development for 30 years, now MRI is one of the most advanced and widely used tools in medical diagnostics.As the essential part of MRI system, spectrometer controls the time sequence, the generation of RF waveform and gradient magnetic field waveform, and transmitting, receiving and processing of signals. There are only a few foreign companies which can provide commercial product. The price is very expensive and the research materials are confidential. At present, a large number of spectrometers are needed to be imported to our country. The MRI System production and maintenance costs are high, and medical examination fees are expensive. Therefore, research and design of homebuilt spectrometer is very important to the development of MRI technology.In this thesis, we conducted thorough researches on MRI theories and spectrometer technology. A software design method of new MRI spectrometer system is provided. We firstly take part in the design program which is concentrated on the design of spectrometer hardware system. Not only do we determine the structure of the hardware system, but also introduce the module function of every hardware module. Next, according the workflow of the spectrometer, we analyze the function of software system. A software design of spectrometer system which runs on a personal computer is provided. Both hardware and software make contributions to satisfying kinds of user requirements. And the spectrometer can obtain a high quality magnetic resonance imaging. This thesis mainly studies on the method of data encapsulation of the MRI sequences and parameters. Moreover, we have realized the reliable communication between main computer and hardware interface card in the spectrometer.The eddy current affects the imaging quality in magnetic resonance imaging systems. In order to improve the quality of MRI imaging, we researched on magnetic resonance imaging eddy current compensation method. After understanding the eddy current generation mechanism and influence of imaging in MRI, we propose an eddy current compensation method based on iterative segmentation calculation. The pre-emphasis of gradient current is an efficient method and is widely used in eddy current compensation. Pre-emphasis of gradient current needs thousands of exponential calculation in a single cycle. So it is imperative to use a rapid method. Iteration calculation is generally used in eddy current compensation. However, accumulated error will be amplified with the number of iterations. In order to solve the problem, based on the fundamental of iteration calculation, an improved iterative segmentation calculation algorithm of eddy current compensation is presented in this thesis. The experiments prove that the accuracy of the pre-emphasis of gradient current is improved effectively with a run-time in the same order of magnitude.