Study On Automatic Gradient Pre-Emphasis Adjustment For MRI Systems

Since Magnetic Resonance Imaging (MRI) appeared in 1973, it has become a routine medical imaging techniques together with X ray, CT, ultrasonic imaging and PET. Compared with the other imaging techniques, MRI has non-invasive and non-ironic properties. Therefore MRI has been widely applied to structural and functional imaging.In recent years, MRI has gotten more and more extensive studies. And the development of MRI techniques requires instrument with higher performance. In this paper, eddy current compensation is investigated in detail.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.A rapid Method of Eddy Current Compensation in Magnetic Resonance Imaging Systems. Imaging Objects are spatially encoding by gradient magnetic fields in magnetic resonance imaging systems. The eddy current caused by rapid switches of gradient fields will result in artifacts in the images. A method of eddy current compensation based on pre-emphasis of gradient current is presented in this thesis. The compensation parameters are acquired rapidly utilizing Faraday's induction theorem and data fitting method. The experiments prove that the method is efficient for reduction of the debugging time and for the improvement of the image quality.Study on Automatic Gradient pre-emphasis Adjustment for MRI Systems. Image distortion caused by eddy currents is a major problem in the imaging system. This distortion may be substantially reduced by careful adjustment of the gradient pre-emphasis unit. A completely automatic method of eddy current compensation based on NMR method is presented in this thesis. This method may find the optimal settings for all three gradient directions in approximately 10 min by fitting and iterative programs. Searching useful signal in advance ensures that the acquisition data is reliable. It is proved that this method is efficient and simple to reduce the debugging time and enhance image quality through OPM35I MRI system.