I was wondering if it is absolutely necessary to do distortion correction for 7T fMRI images?
Due to an error in scanning, there are no fieldmap or reverse phase-encoded images available for correction. I am aware that registration-based correction is possible, but is it a must? I am doing MNI space ROI-based functional connectivity analysis.
Specifically, will it be attacked by reviewers if distortion correction is absent for a 7T fMRI study?
Personally, I doubt a paper would be rejected for lack of SDC, all else being okay, especially if you are doing an ROI based analysis, using more forgiving parcels containing lots of voxels. If you were trying to say that a small cluster of voxels was localized to a certain anatomical region, then I would be more skeptical.
The lack of SDC means that your BOLD and T1w image will not be perfectly aligned (with largest mismatches most likely towards the orbitofrontal and temporal regions). Without knowing more about your goals, this could be relevant for your hypothesis, but that is for you to decide.
This paper can give you some information on the usefulness of SDC for such analyses:
Togo, H.; Rokicki, J.; Yoshinaga, K.; Hisatsune, T.; Matsuda, H.; Haga, N.; Hanakawa, T. Effects of Field-Map Distortion Correction on Resting State Functional Connectivity MRI. Front. Neurosci.2017, 11, 656. https://doi.org/10.3389/fnins.2017.00656.
The paper below compares different SDC method at 7T with no SDC. You can see the impact that SDC makes:
Schallmo, M.; Weldon, K. B.; Burton, P. C.; Sponheim, S. R.; Olman, C. A. Assessing Methods for Geometric Distortion Compensation in 7 T Gradient Echo Functional MRI Data. Hum Brain Mapp2021, 42 (13), 4205–4223. https://doi.org/10.1002/hbm.25540.
The method below can be used in case where no fieldmap was acquired: