title: Inhomogeneous static magnetic field-induced distortion correction applied to diffusion weighted MRI of the breast at 3T.
abstract: OBJECTIVE
  To evaluate the performance of an advanced method for correction of inhomogeneous static magnetic field induced distortion in echo-planar imaging (EPI), applied to diffusion-weighted MRI (DWI) of the breast.
  
  
  METHODS
  An algorithm for distortion correction based on the symmetry of the distortion induced by static field inhomogeneity when the phase encoding polarity is reversed was evaluated in 36 data sets of patients who received an MRI examination that included DWI (b = 0 and 700 s/mm(2) ) and an extra b = 0 s/mm(2) sequence with opposite phase encoding polarity. The decrease of the L2 -square norm after correction between opposed phase encoding b = 0 images was calculated. Mattes mutual information between b = 0 images and fat-suppressed T2 -weighted images was calculated before and after correction.
  
  
  RESULTS
  The L2 -square norm between different phase encoding polarities for b = 0 images was reduced 94.3% on average after distortion correction. Furthermore, Mattes mutual information between b = 0 images and fat-suppressed T2 -weighted images increased significantly after correction for all cases (P < 0.001).
  
  
  CONCLUSIONS
  Geometric distortion correction in DWI of the breast results in higher similarity of DWI to anatomical non-EPI T2 -weighted images and would potentially allow for a more reliable lesion segmentation mapping among different MRI modalities.
authors.affiliation: Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway.|St. Olavs University Hospital, Trondheim, Norway.
authors.forename: Jose R
authors.initials: JR
authors.lastname: Teruel
authors.affiliation: Department of Surgery, St. Olavs University Hospital, Trondheim, Norway.|Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: Hans E
authors.initials: HE
authors.lastname: Fjøsne
authors.affiliation: Clinic of Radiology and Nuclear Medicine, St. Olavs University Hospital, Trondheim, Norway.
authors.forename: Agnes
authors.initials: A
authors.lastname: Østlie
authors.affiliation: Department of Neurosciences, University of California, San Diego, La Jolla, California, USA.
authors.forename: Dominic
authors.initials: D
authors.lastname: Holland
authors.affiliation: Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Neurosciences, University of California, San Diego, La Jolla, California, USA.|Department of Radiology, University of California, San Diego, La Jolla, California, USA.
authors.forename: Anders M
authors.initials: AM
authors.lastname: Dale
authors.affiliation: Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: Tone F
authors.initials: TF
authors.lastname: Bathen
authors.affiliation: Clinic of Radiology and Nuclear Medicine, St. Olavs University Hospital, Trondheim, Norway.|Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: Pål E
authors.initials: PE
authors.lastname: Goa
mesh_terms: D000465:Algorithms; D001940:Breast / Q000033:anatomy & histology*; D001943:Breast Neoplasms / Q000473:pathology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*
keywords: breast; diffusion-weighted imaging; distortion correction; echo-planar imaging