Dear SPMer,
I am a complete newcomer to SPM and I have a question regarding the coregistration step preprocessing my fMRI data. I am not sure whether I should define my mean EPI image as "reference" or as "source" image for coregistration and I found both versions suggested. If I use the mean EPI image as reference and the anatomical image as "source" image the coregistration step takes about half an hour per subject. But if I do it the other way around, defining the anatomical as "reference" image and the mean EPI as "source" image, it takes about 5 hours per subject to coregister - I have huge data set. So I am wondering what the diffrence between these two versions is and in what way I should define the reference and the source image.
I am greatful for any information you have!
Best,
Else
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