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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.

Original publication

DOI

10.1002/mrm.24119

Type

Journal article

Journal

Magn Reson Med

Publication Date

10/2012

Volume

68

Pages

1247 - 1254

Keywords

Algorithms, Artifacts, Brain, Electron Spin Resonance Spectroscopy, Humans, Image Enhancement, Image Interpretation, Computer-Assisted, Reference Values, Reproducibility of Results, Sensitivity and Specificity, Signal Processing, Computer-Assisted