I don't have any ideas here. I think you really need to take a close
look at the data. You can read the fields in the headers by:
P='blah.nii';
Nii=nifti(P)
If you want to see the actual values, then you can look at a hidden
field of the nifti object:
Nii.hdr
Computing difference images via ImCalc, and displaying them via
CheckReg can also help to give clues.
Best regards,
-John
On 24 November 2011 10:53, Joshua Balsters <[log in to unmask]> wrote:
> 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
>
