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Abstract #3281

On the source of unresolved Nyquist ghosting in EPI at high and ultrahigh field

Hannah Scholten1, Istvan Homolya2, and Herbert Köstler1
1Institute of Diagnostic and Interventional Radiology, University Hospital Würzburg, Würzburg, Germany, 2Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center, University Hospital Würzburg, Würzburg, Germany

Synopsis

Keywords: Gradients, System Imperfections: Measurement & Correction, Echo-planar imaging

Motivation: Residual Nyquist ghosting commonly confounds echo-planar images at ultrahigh field. The effect is not yet fully understood.

Goal(s): To elucidate why standard ghost correction methods may fail at 7T.

Approach: We analyzed the shift between odd and even echoes based on a linear, time-invariant (LTI) gradient model for different gradient axes and field strengths. In EPI experiments, we quantified the artifacts for corrections based on three navigators and the LTI-model.

Results: Mechanical resonances of the gradient coils cause oscillating shifts between odd and even echoes. Through appropriate parameter choices or trajectory correction, they can be avoided or corrected for.

Impact: Residual Nyquist ghosting in EPI at 7T can be reduced by avoiding or correcting for mechanical oscillations of the gradient coils. A deepened understanding of this effect allows for more reliable correction strategies and less confounded functional or diffusion-weighted MRI.

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Keywords