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Publications

Journal Article Ppublish

PubMed: 40173320 DOI: 10.1002/mrm.30489

Short-term gradient imperfections in high-resolution EPI lead to Fuzzy Ripple artifacts.

Magn Reson Med 94(2):571-587

Authors: Laurentius Renzo Huber, Rüdiger Stirnberg, A Tyler Morgan, David A Feinberg, Philipp Ehses, Lasse Knudsen, Omer Faruk Gulban, Kenshu Koiso, Isabel Gephart, Stephanie Swegle, Susan G Wardle, Andrew S Persichetti, Alexander J S Beckett, Tony Stöcker, Nicolas Boulant, Benedikt A Poser, Peter A Bandettini

Affiliations

  • NIMH, NIH, Bethesda, Maryland, USA.
  • German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
  • Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California, USA.
  • Advanced MRI Technologies, Sebastopol, California, USA.
  • Center of Functionally Integrative Neuroscience (CFIN), Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.
  • Sino-Danish Center for Education and Research (SDC), University of Chinese Academy of Sciences, Beijing, China.
  • Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.
  • Brain Innovation, Maastricht, The Netherlands.
  • University Paris Saclay, CEA, CNRS, NeuroSpin, BAOBAB, Gif-sur-Yvette, France.

Abstract

PURPOSE

High-resolution fMRI is a rapidly growing research field focused on capturing functional signal changes across cortical layers. However, the data acquisition is limited by low spatial frequency EPI artifacts; termed here as Fuzzy Ripples. These artifacts limit the practical applicability of acquisition protocols with higher spatial resolution, faster acquisition speed, and they challenge imaging in inferior regions of the brain.

METHODS

We characterize Fuzzy Ripple artifacts across commonly used sequences and distinguish them from conventional EPI Nyquist ghosts and off-resonance effects. To investigate their origin, we employ dual-polarity readouts.

RESULTS

Our findings indicate that Fuzzy Ripples are primarily caused by readout-specific imperfections in k-space trajectories, which can be exacerbated by short-term eddy current, and by inductive coupling between third-order shims and readout gradients. We also find that these artifacts can be mitigated through complex-valued averaging of dual-polarity EPI or by disconnecting the third-order shim coils.

CONCLUSION

The proposed mitigation strategies allow overcoming current limitations in layer-fMRI protocols: Achieving resolutions beyond 0.8 mm is feasible, and even at 3T, we achieved 0.53 mm voxel functional connectivity mapping. Sub-millimeter sampling acceleration can be increased to allow sub-second TRs and laminar whole brain protocols with up to GRAPPA 8. Sub-millimeter fMRI is achievable in lower brain areas, including the cerebellum.

MeSH

Brain

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