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Year of Publication: 2024
Project: Layer Specific fMRI
FIM Authors:
Authors:
  • Laurentius Huber
  • Rüdiger Stirnberg
  • Tyler Morgan
  • David A. Feinberg
  • Philipp Ehse
  • Lasse Knudsen
  • Omer Faruk Gulban
  • Kenshu Koiso
  • Stephanie Swegle
  • Isabel Gephart
  • Susan G. Wardle
  • Andrew Persichetti
  • Alexander JS Beckett
  • Tony Stöcker
  • Nicolas Boulant
  • Benedikt A. Posner
  • Peter Bandettini
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 lower brain areas.

Methods: We characterize Fuzzy Ripple artifacts across commonly used sequences and distinguish them from conventional EPI Nyquist ghosts, off-resonance effects, and GRAPPA artifacts. 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 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: (1)Achieving resolutions beyond 0.8mm is feasible, and even at 3T, we achieved 0.53mm voxel functional connectivity mapping. (2) Sub-millimeter sampling acceleration can be increased to allow sub-second TRs and laminar whole brain protocols with up to GRAPPA 8. (3)Sub-millimeter fMRI is achievable in lower brain areas, including the cerebellum.


Data
Code
Journal: BioRXiv
URL: https://pmc.ncbi.nlm.nih.gov/articles/PMC11418939/
DOI: https://doi.org/10.1101/2024.09.04.611294