Improvements Of Liver Quantitative Susceptibility Mapping

Quantitative susceptibility mapping(QSM)can deconvolve the blooming artifacts in GRE phase data to determine tissue magnetic susceptibility distribution.QSM has recently been applied to abdominal organs by additionally accounting for the fat contribution to the measured signal phase.In this thesis,some investigations were performed to solve the challenges to liver QSM.The main contents are as follows:1.Optimization of Pulse Sequence Parameters for Liver QSMThe effects of scanning parameters on the accuracy of water-fat separation and quantitative susceptibility were investigated by theoretical analysis,numerical simulation and human abdominal experiments.The results show that the echo times,spatial uniformity correction,flip angle and receiver bandwidth can affect the accuracy of water-fat separation and magnetic susceptibility.Based on these investigations,criterions for gradient echo sequence parameters selection and some recommended parameters have been provided in liver QSM.2.Phase Correction for Liver Quantitative Susceptibility Mapping Using Bipolar Gradients SequenceBipolar acquisition in liver QSM introduces phase errors between odd and even echoes that can cause inaccuracies in susceptibility estimation.To solve this problem,we proposed a method in the image domain to efficiently correct the phase error.Both numerical simulations and human abdominal experiments demonstrate that the proposed algorithm can effectively correct the odd-even echo phase difference and obtain a more accurate quantitative susceptibility,R2* and PDFF maps.3.Selection of Reference Regions for Liver QSMQSM only determines susceptibility differences rather than absolute susceptibility values.This study proposed the water in the stomach as a reference and investigated the stability of susceptibility values in various tissues in abdomen estimated using liver QSM.The results show that the susceptibility of water in the stomach drinking after an overnight fasting is stable and changes little among the individuals,which would potentially be the best reference for susceptibility value.