• Guoxiang Liu and Seiji Ogawa.
• Brain Information Group, National Institute of Information and Communications Technology, Kobe, Hyougo, Japan. lgx@po.nict.go.jp
• J Magn Reson Imaging. 2006 Sep 1; 24 (3): 683-9.

PurposeTo derive and implement a method for correcting geometric distortions and recovering magnetic resonance imaging (MRI) signal losses caused by susceptibility-induced magnetic field gradients (SFGs) in regions with large static field inhomogeneities in echo-planar imaging (EPI).Materials And MethodsFactors to account for field inhomogeneities and SFGs were added in a traditional EPI equation that was a simple Fourier transform (FT) for expressing the actual k-space data of an EPI scan. The inverse calculation of this "distorted EPI" equation was used as a kernel to correct geometric distortions and reductions in intensity during reconstruction. A step-by-step EPI reconstruction method was developed to prevent complicated phase unwrapping problems. Some EPI images of phantom and human brains were reconstructed from standard EPI k-spaces.ResultsAll images were reconstructed using the proposed multistep method. Geometric distortions were corrected and SFG-induced MRI signal losses were recovered.ConclusionResults suggest that applying our method for reconstructing EPI images to reduce distortions and MRI signal losses is feasible.

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