Hi pt,

Here are my answers to your questions:

0) are these 3D volumes, or 2D slices? - 2D slices
1) what are the voxel dimensions of the data? - anisotropic 1x1x3 mm voxels (1x1 in the axial plane)
2) how much distortion/difference is there from time point to time point? - it depends on the task, but the cord can regularly move 0-3 mm (mostly in the ventral-dorsal direction)
3) how you are evaluating these (visualizing overlay/underlay, for example), and what means better or worse (boundaries line up, features lining up, less blurry)? - I have been using tSNR as one metric to evaluate these. I also will visually compare the fMRI timeseries before/after motion correction. I tend to look for whether the spinal cord/CSF region/boundary is remaining in the same location from timepoint to timepoint.
4) would you be able to share the data, if I sent a Box drive to your email? It is hard to advise on something I am not very familiar with. For example, I might try the 'lpa' or 'nmi' cost function, but those choices are informed from a very different context. - Thank you! I should probably be able to share some data. Should I private message you to provide my email?

Best,
Kim