Hi,

I have a question about within- vs. between-run motion. Attached is the plot of the six motion parameters of one of our participants, obtained using 3dvolreg with the very first functional volume as the base volume (six runs in total). This participant had very little within-run motion (less than 1 mm) but substantial between-run motion between runs 3 and 4. In another thread on this message board I read that "between run motion is considered irrelevant" (http://afni.nimh.nih.gov/afni/community/board/read.php?1,141952,141953#msg-141953).

Could you explain why between-run motion is less relevant than within-run motion?

And how can we prevent excluding this participant on the basis of our excessive motion criterion (> 3 mm or degrees motion leads to exclusion). Should we run 3dvolreg with the first volume of each run (instead of the first volume of each session) as the base volume?

Thanks in advance for your reply,
Sandra Langeslag