title: A new EPI-based dynamic field mapping method: application to retrospective geometrical distortion corrections.
abstract: OBJECTIVE
  To retrospectively correct for geometrical distortions, a new dynamic field mapping method suitable for dynamic single-shot gradient-echo type echo-planar imaging (GRE-EPI) is proposed.
  
  
  METHODS
  The method requires a single volume additional acquisition and allows the extraction of a field map from each phase volume, assuming invariance across time of the echo time-independent phase component. Performances of the method are assessed using three sets of experiments: the first tests the prerequisite and the modeling; the second tests the method with time-dependent geometrical distortions; and the third presents a comparison with two other methods.
  
  
  RESULTS
  Our results legitimize the modeling procedure and demonstrate that the dynamic method is less sensitive to noise than the other methods. A theoretical explanation for this is proposed in the discussion section.
  
  
  CONCLUSIONS
  Given the minor increase in the acquisition time, this method is well suited for functional magnetic resonance imaging; prospective direction.
authors.affiliation: Unité Mixte de Recherche (UMR)6194 Centre National de Recherche Scientifique (CNRS), Commissariat à l'Energie Atomique (CEA), Université de Caen et Paris 5, Caen, France.
authors.forename: Franck
authors.initials: F
authors.lastname: Lamberton
authors.forename: Nicolas
authors.initials: N
authors.lastname: Delcroix
authors.forename: Denis
authors.initials: D
authors.lastname: Grenier
authors.forename: Bernard
authors.initials: B
authors.lastname: Mazoyer
authors.forename: Marc
authors.initials: M
authors.lastname: Joliot
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000473:pathology; D001931:Brain Mapping; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional / Q000379:methods; D019047:Phantoms, Imaging; D012044:Regression Analysis; D012189:Retrospective Studies; D012984:Software