MRI raw data to publication: Fuzzy ripple artifact in high resolution fMRI: identification, cause, and mitigation.

These Data are refering to the maunscript "Fuzzy ripple artifact in high resolution fMRI: identification, cause, and mitigation" authored by 

Renzo Huber1, Rüdiger Stirnberg2, A Tyler Morgan1, David A Feinberg3,4-5, Samantha J Ma6, Philipp Ehses3, Omer Faruk Gulban2,7, Kenshu Koiso2, Isabel Gephart1, Stephanie Swegle1, Susan Wardle1, Emily Ma2, Andrew Persichetti1, Alexander JS Beckett4-5, Tony Stöcker3, Nicolas Boulant8, Benedikt A Poser2, Peter Bandettini1

1 NIMH, NIH, Bethesda, United States,

2 German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany,

3 Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA, United States, 

4 Advanced MRI Technologies, Sebastopol, CA, United States,

5 CN, FPN, University of Maastricht, The Netherlands,

6 Siemens Medical Solutions USA, Inc., Berkeley, CA, USA,

7 Brain Innovation, Maastricht, The Netherlands,

8 CEA, NeuroSpin, University Paris Saclay, France.

Abstract

Purpose: High resolution fMRI is an emerging research field focused on capturing functional signal changes across cortical layers. However, the data acquisition is limited by low spatial frequency EPI artifacts; termed 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 kx-specific imperfections in gradient 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.

Conclusion: The proposed mitigation strategies allow for 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) Temporal acquisition speed can be increased to GRAPPA 8. 

(3) Sub-millimeter fMRI is achievable in lower brain areas, including the cerebellum.