Hi, Naveed-

This is a pretty tough thing to try to speculate on, because several things could be happening.

From your separate communication, it sounds like there is a difference in acquisitions here as well, with the "problem" data using multiband data. It is possible that that could be causing headaches, either via header information not being correct, or by having correlation across selected slices. I have never worked with multiband FMRI data, but my guess is that subtleties with this could be occurring here, starting from DICOM conversion.

I think in general that if this question were phrased about asking for suggestions in processing multiband data, others with experience in that particular area might be able offer suggestions.

Other things to possibly check:

You appear to have very high correlation across ROIs-- I will assume that you have checked the mapping/locations of those, and those are OK? Alignment to anatomical and segmentation are OK?

Something perhaps to try is using @radial_correlate on your time series, even before processing, to see if there are large patches of high correlation in your data sets? (With the idea being that there might be a leakage across slices or something?)

Also, have you converted the DICOMs in any particular way?

-pt