• Wietske van der Zwaag, José P Marques, Hongxia Lei, Nathalie Just, Tobias Kober, and Rolf Gruetter.
• Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Switzerland. wietske.vanderzwaag@epfl.ch
• J Magn Reson Imaging. 2009 Nov 1; 30 (5): 1171-8.

PurposeTo 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 MethodsAn 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.ResultsIrrespective 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.ConclusionIt 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.

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