Dear Christopher and Michael,
the voxel size was 3 mm in-plane and slice thickness 3 mm + 15% gap = 3.45 mm. Realignment was onto the mean, if that's of relevance.
Yes, there's not much motion going on indeed. I just took a random data set lying around to check what Stefan mentioned, so just for visualization purpose. I have encountered different RPs depending on the (re-)orientation of the EPIs previously, but didn't further examine it at that time. Basically, if the origin is different, then I'd say the rotation parametres should be different. Here it's the other way round, same rotation parametres but different translation parametres. But this might be a logical error, depending on which parametres are applied first.
By the way, I've already been wondering what x y z actually stand for in the context of realign & unwarp. World space? Voxel space? See https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind1306&L=spm&F=&S=&P=216973 But there's no answer so far. Based on the finding above it seems the header information about the position is not ignored (no idea whether that's good or bad or irrelevant). Otherwise it shouldn't matter whether volumes are translated / rotated before.
Best,
Helmut
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