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Related Experiment Videos

The effect of residual Nyquist ghost in quantitative echo-planar diffusion imaging.

D A Porter1, F Calamante, D G Gadian

  • 1Radiology and Physics Unit, Institute of Child Health, University College London Medical School, London, United Kingdom.

Magnetic Resonance in Medicine
|August 10, 1999
PubMed
Summary

Residual Nyquist ghosts in echo-planar imaging (EPI) can create misleading low apparent diffusion coefficient (ADC) values in diffusion studies. Spatial presaturation or fluid-suppression techniques effectively prevent these artifacts in diffusion-weighted EPI scans.

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Area of Science:

  • Magnetic Resonance Imaging
  • Medical Physics
  • Radiology

Background:

  • Single-shot echo-planar imaging (EPI) is standard for diffusion studies due to motion insensitivity.
  • Residual Nyquist ghosts, though reduced, can still impact image quality in EPI.
  • These ghosts can lead to artifacts in apparent diffusion coefficient (ADC) mapping.

Purpose of the Study:

  • To identify and characterize artifacts in ADC maps caused by Nyquist ghosts in diffusion-weighted EPI.
  • To demonstrate that these artifacts can simulate true regions of reduced diffusion.
  • To propose methods for mitigating these artifacts in clinical practice.

Main Methods:

  • In vivo diffusion-weighted EPI data were acquired.
  • Phantom studies were conducted to analyze ghost properties (phase and amplitude).

Related Experiment Videos

  • Theoretical expressions were used to understand artifact generation.

    • Main Results:

    • Residual Nyquist ghosts in EPI create artifacts appearing as regions of low ADC.
    • These artifacts are b-value dependent and mimic reduced diffusion.
    • Spatial presaturation and fluid-suppression successfully eliminated the artifacts in vivo.

    Conclusions:

    • Nyquist ghosts in diffusion-weighted EPI pose a significant artifact risk in ADC quantification.
    • Standard presaturation or fluid-suppression methods are effective countermeasures.
    • This phenomenon is likely prevalent in current commercial MRI scanners and requires consideration in diffusion studies.