Magnetic Resonance Phase Information Processing And Its Application In Susceptibility Weighted Imaging

Magnetic Resonance Imaging (MRI) is used a quadrature detection, which can provide a magnitude image and a phase image of a same level. Although the phase image contains a lot of useful information, but the amplitude image is mainly used in the MRI. Phase information except to being used in the quantitative analysis of blood flow in large vessels and the inversion recovery sequence of water separation from fat and the susceptibility weighted imaging (SWI) is almost lost. There are two main reasons:(1) MR phase information is susceptible to artifacts interfere that cause from magnetic field inhomogeneity and the inconsistency between the air and soft tissue at the junction and bone and soft tissue at the junction,which is called background artifacts, the background artifacts will mask the useful information;(2) Phase is intertwined to (-π,π], that is not the true phase. Therefore, in order to get useful of phase image for medical research and clinical diagnostic, we need to do a series processing to phase image.Susceptibility weighted imaging(SWI) is used the phase information extracted from the phase image to weighted the amplitude image, which enhances the contrast of the amplitude image. The key of the SWI is that how MR phase is processed. The investigation of the magnetic resonance phase information processing method has an important role in promoting the SWI technology development.This dissertation is described the traditional susceptibility weighted imaging method and the processing method of the magnetic resonance phase, and also is analyzed its limitation. Then, I bring MR phase information processing method based on the phase unwrapping and apply it to the susceptibility weighted imaging. In the dissertation, I use branch cut and quality map guide method to unwrapping the phase to achieve the susceptibility weighted imaging. The detailed steps are as follows:(1) Use the branch cut method or quality map guide method to unwrapping the phase in the MR phase image.(2) Make a high-pass filter to filter out low frequency interference of the Unwrapped phase image.(3) Make the phase mask.(4) Obtain the susceptibility weighted image through weighted to amplitude image. According to the above processing principle, I use MATLAB software to make the corresponding program to processing the clinical magnetic resonance images, both of the methods are obtained SWI images successful. The image quality is improved compared to the traditional magnetic susceptibility weighted imaging method. Compared with the three methods, the quality map guide method gets the best image, but takes the most running time. Then the branch cut method, the traditional susceptibility weighted imaging method gets the shortest running time but the worst image quality.