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Reference‐free unwarping of EPI data using dynamic off‐resonance correction with multiecho acquisition (DOCMA)
Author(s) -
Visser Eelke,
Poser Benedikt A.,
Barth Markus,
Zwiers Marcel P.
Publication year - 2012
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.24119
Subject(s) - distortion (music) , echo planar imaging , computer science , data acquisition , echo (communications protocol) , volume (thermodynamics) , signal (programming language) , planar , echo time , magnetic resonance imaging , computer vision , nuclear magnetic resonance , artificial intelligence , algorithm , physics , computer graphics (images) , medicine , computer network , amplifier , bandwidth (computing) , quantum mechanics , radiology , programming language , operating system
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. Magn Reson Med 2012. © 2011 Wiley Periodicals, Inc.