Reference-free unwarping of EPI data using dynamic off-resonance correction with multiecho acquisition (DOCMA)
SourceMagnetic Resonance in Medicine, 68, 4, (2012), pp. 1247-1254
Article / Letter to editor
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Donders Centre for Cognitive Neuroimaging
PI Group MR Techniques in Brain Function
F.C. Donders Centre for Cognitive Neuroimaging
Magnetic Resonance in Medicine
Subject150 000 MR Techniques in Brain Function; 150 003 International high field MRI Centre Essen; DCN PAC - Perception action and control
Inhomogeneities 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.
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