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Minimization of Nyquist ghosting for echo‐planar imaging at ultra‐high fields based on a “negative readout gradient” strategy
Author(s) -
van der Zwaag Wietske,
Marques José P.,
Lei Hongxia,
Just Nathalie,
Kober Tobias,
Gruetter Rolf
Publication year - 2009
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.21951
Subject(s) - ghosting , echo planar imaging , scanner , physics , imaging phantom , computer science , nuclear magnetic resonance , signal (programming language) , nyquist frequency , planar , magnetic resonance imaging , functional magnetic resonance imaging , artificial intelligence , computer vision , optics , medicine , radiology , computer graphics (images) , filter (signal processing) , programming language
Purpose: To improve the traditional Nyquist ghost correction approach in echo planar imaging (EPI) at high fields, via schemes based on the reversal of the EPI readout gradient polarity for every other volume throughout a functional magnetic resonance imaging (fMRI) acquisition train. Materials and Methods: An EPI sequence in which the readout gradient was inverted every other volume was implemented on two ultrahigh‐field systems. Phantom images and fMRI data were acquired to evaluate ghost intensities and the presence of false‐positive blood oxygenation level‐dependent (BOLD) signal with and without ghost correction. Three different algorithms for ghost correction of alternating readout EPI were compared. Results: Irrespective of the chosen processing approach, ghosting was significantly reduced (up to 70% lower intensity) in both rat brain images acquired on a 9.4T animal scanner and human brain images acquired at 7T, resulting in a reduction of sources of false‐positive activation in fMRI data. Conclusion: It is concluded that at high B 0 fields, substantial gains in Nyquist ghost correction of echo planar time series are possible by alternating the readout gradient every other volume. J. Magn. Reson. Imaging 2009;30:1171–1178. © 2009 Wiley‐Liss, Inc.