Gradient-echo EPI distortions correction using a over-sampling low-ky pulse sequence and k-space energy spectrum analysis
Date Issued
2007
Date
2007
Author(s)
Chiu, Su-Chin
DOI
en-US
Abstract
The geometric distortion in echo-planar imaging (EPI) and its correction are systematically investigated in this thesis. EPI is one of the fastest MRI acquisition pulse sequence and is widely used for dynamic studies. However, in the presence of the field inhomogeneities, the EPI k-space energy peaks are displaced, which result in geometric distortions in the reconstructed images. Here we use the k-space energy spectrum analysis to calculate the k-space energy displacement in EPI. The calculated k-space energy displacement map can be converted to the field inhomogeneity map, which can then be applied to correct the EPI distortions using a phase modulation post-processing procedure. The EPI data corrected with the previously developed k-space energy spectrum based method, however, may have residual distortions due to an unknown B0 reference and the accumulated errors during the integration procedure. To further improve the accuracy and reliability of EPI distortion correction, we propose to combine the k-space energy spectrum analysis and an altered EPI acquisition strategy, in which the central part of the k-space is double sampled. In this approach, the B0 reference can be obtained from the embedded low-resolution double-TE data. In addition, the error accumulation in the integration procedure can be minimized.
Experimental results show that the new method can effectively remove EPI geometric distortions.
Subjects
磁振造影
平面回訊影像
幾何扭曲修正
K空間能量頻譜
Magnetic Resonance Imaging
MRI
Echo-Planar Imaging
EPI
Geometrical distortion
k-space energy spectrum
Type
thesis
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