Correction for EPI distortions using multi-echo gradient-echo imaging.
A novel and effective technique is described for distortion correction in echo planar imaging (EPI) utilizing the field maps derived from multi-echo gradient-echo images. The distortions from different off-resonance related factors such as field inhomogeneity, eddy current effect, radiofrequency pulse frequency offset, and chemical shift effect can be simultaneously reduced to a great extent. With the proposed post-processing algorithm of multi-channel modulation, distortions may be corrected without unwrapping the phase discontinuities in the derived field map, a process that usually restricts the application of other field map-based correction methods. Results from phantom and animal experiments at 4.7 T demonstrate the efficiency of the method in reducing the geometrical distortions in gradient-echo EPI.
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