title: EPI image reconstruction with correction of distortion and signal losses.
abstract: OBJECTIVE
  To 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).
  
  
  METHODS
  Factors 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.
  
  
  RESULTS
  All images were reconstructed using the proposed multistep method. Geometric distortions were corrected and SFG-induced MRI signal losses were recovered.
  
  
  CONCLUSIONS
  Results suggest that applying our method for reconstructing EPI images to reduce distortions and MRI signal losses is feasible.
authors.affiliation: Brain Information Group, National Institute of Information and Communications Technology, Kobe, Hyougo, Japan. lgx@po.nict.go.jp
authors.forename: Guoxiang
authors.initials: G
authors.lastname: Liu
authors.forename: Seiji
authors.initials: S
authors.lastname: Ogawa
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000473:pathology; D001931:Brain Mapping; D017352:Echo-Planar Imaging / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D015233:Models, Statistical; D019047:Phantoms, Imaging; D011381:Programming Languages; D012984:Software