title: PSF mapping-based correction of eddy-current-induced distortions in diffusion-weighted echo-planar imaging.
abstract: OBJECTIVE
  To accurately correct diffusion-encoding direction-dependent eddy-current-induced geometric distortions in diffusion-weighted echo-planar imaging (DW-EPI) and to minimize the calibration time at 7 Tesla (T).
  
  
  METHODS
  A point spread function (PSF) mapping based eddy-current calibration method is newly presented to determine eddy-current-induced geometric distortions even including nonlinear eddy-current effects within the readout acquisition window. To evaluate the temporal stability of eddy-current maps, calibration was performed four times within 3 months. Furthermore, spatial variations of measured eddy-current maps versus their linear superposition were investigated to enable correction in DW-EPIs with arbitrary diffusion directions without direct calibration. For comparison, an image-based eddy-current correction method was additionally applied. Finally, this method was combined with a PSF-based susceptibility-induced distortion correction approach proposed previously to correct both susceptibility and eddy-current-induced distortions in DW-EPIs.
  
  
  RESULTS
  Very fast eddy-current calibration in a three-dimensional volume is possible with the proposed method. The measured eddy-current maps are very stable over time and very similar maps can be obtained by linear superposition of principal-axes eddy-current maps. High resolution in vivo brain results demonstrate that the proposed method allows more efficient eddy-current correction than the image-based method.
  
  
  CONCLUSIONS
  The combination of both PSF-based approaches allows distortion-free images, which permit reliable analysis in diffusion tensor imaging applications at 7T.
authors.affiliation: Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Germany.
authors.forename: Myung-Ho
authors.initials: MH
authors.lastname: In
authors.affiliation: Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Germany.
authors.forename: Oleg
authors.initials: O
authors.lastname: Posnansky
authors.affiliation: Department of Biomedical Magnetic Resonance, Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Germany.|German Centre for Neurodegenerative Diseases (DZNE), Site Magdeburg, Germany.|Leibniz Institute for Neurobiology, Magdeburg, Germany.|Center for Behavioral Brain Sciences, Magdeburg, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Speck
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging; D001931:Brain Mapping / Q000379:methods*; D002138:Calibration; D038524:Diffusion Magnetic Resonance Imaging; D056324:Diffusion Tensor Imaging; D017352:Echo-Planar Imaging; D006801:Humans; D021621:Imaging, Three-Dimensional
keywords: DTI; EPI; PSF; eddy-current; geometric distortion