Dear SPMers
I found one previous discussion on this point but not much else, so apologies if I'm repeating what everyone already knows.
I've recently starting using 4D files straight from the scanner (Philips Acheiva) in SPM rather than splitting them into 3D files using fslsplit. I'm finding in most cases there are subtle (+/-0.5mm) to drastic (over 2mm) differences in my realignment parameters depending on whether I use the 4D or 3D versions of the same datasets. These differences are only in the translations and not the rotations.
It would be great if anyone could explain why this happens. I had a quick look for differences between the 3D and 4D files and I think the issue is that fslplit is automatically changing my datatype from int16 to float32, and i read in a previous discussion that it also changes the scaling factor which is probably the bigger issue.
any advice on this issue would be greatly appreciated!
Best
Josh
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