Two-dimensional phase cycled reconstruction for inherent correction of echo-planar imaging nyquist artifacts

Nan Kuei Chen, Alexandru V. Avram, Allen W. Song

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


The inconsistency of k-space trajectories results in Nyquist artifacts in echo-planar imaging (EPI). Traditional techniques often only correct for phase errors along the frequency-encoding direction (one-dimensional correction), which may leave significant residual artifacts, particularly for oblique-plane EPI or in the presence of cross-term eddy currents. As compared with one-dimensional correction, two-dimensional (2D) phase correction can be much more effective in suppressing Nyquist artifacts. However, most existing 2D correction methods require reference scans and may not be generally applicable to different imaging protocols. Furthermore, EPI reconstruction with these 2D phase correction methods is susceptible to error amplification due to subject motion. To address these limitations, we report an inherent and general 2D phase correction technique for EPI Nyquist removal. First, a series of images are generated from the original dataset, by cycling through different possible values of phase errors using a 2D reconstruction framework. Second, the image with the lowest artifact level is identified from images generated in the first step using criteria based on background energy in sorted and sigmoid-weighted signals. In this report, we demonstrate the effectiveness of our new method in removing Nyquist ghosts in single-shot, segmented and parallel EPI without acquiring additional reference scans and the subsequent error amplifications.

Original languageEnglish (US)
Pages (from-to)1057-1066
Number of pages10
JournalMagnetic Resonance in Medicine
Issue number4
StatePublished - Oct 2011
Externally publishedYes


  • 2D phase correction
  • Nyquist artifacts
  • echo-planar imaging
  • phase-cycled reconstruction

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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