• Eelke Visser, Benedikt A Poser, Markus Barth, and Marcel P Zwiers.
• Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Department of Cognitive Neuroscience, Nijmegen, The Netherlands. eelke.visser@donders.ru.nl
• Magn Reson Med. 2012 Oct 1; 68 (4): 1247-54.

AbstractInhomogeneities of the main magnetic field cause geometric distortion in echo-planar imaging, a method central to functional MRI. A number of correction methods have been proposed, most of which are based on the acquisition of a fieldmap providing the local offsets to the main magnetic field. Here, accelerated multiecho echo-planar imaging is used, with echo times short enough to enable the construction of a fieldmap of comparable quality from the data themselves. This way, each volume in a time series can be unwarped using a fieldmap obtained from that volume, avoiding volume-to-volume field-motion interactions that invalidate reference data in conventional approaches that use a single, static, fieldmap. The combination of accelerated acquisition with dynamic distortion correction yields volumes with very low distortion at repetition times similar to conventional echo-planar imaging. The method is applied to data acquired at 3 and 7 T and is shown to effectively correct image geometry. Furthermore, it is shown that dynamic distortion correction yields better temporal signal stability than correction using a static fieldmap in the presence of subject motion.Copyright © 2011 Wiley Periodicals, Inc.

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