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EPI Nyquist ghost and geometric distortion correction by two-frame phase labeling.

Victor B Xie1,2, Mengye Lyu1,2, Ed X Wu1,2

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Summary

A new method effectively corrects Nyquist ghost and geometric distortion in echo planar imaging (EPI) using parallel imaging. This technique significantly improves image quality for dynamic EPI applications.

Keywords:
EPI artifactsNyquist ghost correctionfMRIgeometric distortion correctionparallel imaging

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Area of Science:

  • Magnetic Resonance Imaging
  • Image Reconstruction
  • Medical Physics

Background:

  • Echo planar imaging (EPI) is susceptible to artifacts like Nyquist ghost and geometric distortion.
  • Existing correction methods may be insufficient, especially under challenging imaging conditions.

Purpose of the Study:

  • To develop and evaluate a novel method for correcting Nyquist ghost and geometric distortion in EPI.
  • The method leverages parallel imaging techniques for enhanced correction.

Main Methods:

  • Acquisition of two EPI data frames: one normal and one phase-labeled.
  • Utilizing GRAPPA (Generalized Autocalibrating Partially Parallel Acquisition) to train weights for Nyquist ghost removal.
  • Generating a B0 field map from phase differences for geometric distortion correction.

Main Results:

  • Significant reduction in Nyquist ghosting across various imaging conditions, outperforming existing methods.
  • Complete restoration of image geometry after distortion correction.
  • Preservation of signal-to-noise ratio efficiency and no apparent degradation of temporal resolution in fMRI.

Conclusions:

  • The developed method offers robust correction for both Nyquist ghost and geometric distortion in EPI.
  • This technique is particularly well-suited for dynamic EPI applications requiring high-quality imaging.