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Robust field map generation using a triple‐echo acquisition
Author(s) -
Windischberger Christian,
Robinson Simon,
Rauscher Alexander,
Barth Markus,
Moser Ewald
Publication year - 2004
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.20158
Subject(s) - distortion (music) , multislice , computer science , echo (communications protocol) , pixel , echo planar imaging , phase (matter) , artificial intelligence , field (mathematics) , magnetic resonance imaging , set (abstract data type) , computer vision , nuclear magnetic resonance , physics , mathematics , medicine , computer network , amplifier , bandwidth (computing) , quantum mechanics , pure mathematics , radiology , programming language
Purpose To establish a fast and robust technique for generating magnetic field maps for the correction of geometric distortions in echo‐planar magnetic resonance (MR) images. Materials and Methods Multislice gradient‐echo (GE) images were acquired at echo times of 6, 6.5, and 7.5 msec in order to cover a field shift range of ±666 Hz in the resulting B 0 maps. To account for possible phase wrap scenarios, seven phase triples were calculated for each pixel. Linear regression of the phase vs. echo time was performed for each set. The slope of the set with the minimum fitting error was taken as the true magnetic field in the respective pixel. Results Based on the fitting error distribution, the technique is shown to be feasible and effective for assessing the field distribution in the brain at 3 T, especially in inferior brain areas (amygdalae, hippocampus). Examples of echo‐planar images distortion corrected using the calculated field maps are shown. Conclusion The approach presented yields robust estimation of magnetic field maps and requires under a minute of additional acquisition time and only seconds of computational time. As such, it is easily possible to apply image distortion correction in routine functional MR imaging (fMRI) studies, enabling improved coregistration of brain activation maps with structures on anatomical images. J. Magn. Reson. Imaging 2004;20:730–734. © 2004 Wiley‐Liss, Inc.