Preliminary Study On Quantitative Susceptibility Mapping Via Single-scan Spatiotemporally Encoded MRI

Magnetic resonance imaging (MRI) which is based on the nuclear magnetic resonance (NMR) can provide a no damaged means to detect structure in vivo. Echo planar imaging (EPI) has the ability to acquire a whole image in a single-scan, but it is sensitive to susceptibility artifacts when it is operated in high or inhomogeneous magnetic field. Therefore, EPI is usually not suitable for phase imaging. Single-scan spatiotemporally encoded (SPEN) MRI is one of the effective approaches in dealing with this weakness. It has a higher natural immunity to field inhomogeneity and can provide image with similar quality to that from EPI method in homogeneous field. Quantitative susceptibility mapping (QSM) based on phase information is a hot question in scientific research and clinical application now. This paper proposed a local phase imaging method based on single-scan SPEN method, which will be of significance in promoting QSM having deeper and broader applications. The main work of this thesis is listed as follows.1. This paper firstly has a brief introduction of QSM principle. Then a comprehensive review was made about the methods of the typical reconstruction methods of QSM and background field removal methods, then a summary was presented about the applications of QSM in MRI.2. The reconstruction of QSM based on conventional sampling method was accomplished. Multi-echo pulse sequence was used to obtain FID data, Multi-echo data could provide more phase information which would be helpful in the reconstruction of QSM. This paper used l0norm of gradient method to reconstruct the QSM images, and the results were discussed and compared.3. A fully refocused SPEN sequence was applied to local phase imaging researches for the first time, which could make the decoding signals from different positions get refocused about gradient and off-resonance, and the results of different samples had been analyzed and discussed, including SPIO sample, lemon sample and pig brain sample. The feasibility of applying this fully refocused SPEN sequence to local phase imaging researches was verified, which will provide sampling method for single-scan dynamic QSM.