Eelke Visser1,2, Benedikt A. Poser3, Markus Barth1,4, Marcel P. Zwiers1,2
1Donders Institute for Brain, Cognition & Behaviour, Radboud University Nijmegen, Nijmegen, Netherlands; 2Department of Cognitive Neuroscience, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands; 3Department of Medicine, Queen's Medical Center, Honolulu, HI, United States; 4Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
Inhomogeneities of the main magnetic field are known to cause considerable geometric distortion of EPI-acquired data. Accelerated acquisition reduces the problem, but does not eliminate it. We calculate field maps directly from the phase maps of the first two echoes in a multi echo EPI acquisition and use these to correct the residual distortions. The resulting geometrical fidelity yields a significant improvement in the co-registration to undistorted data.