Hi Daniel,

Thank you for the clarification and response. If I may explain my situation a bit further, I think it might help to clarify what I mean by merge. So the two data sets I have are time points 1 and time points 2. After I have reoriented the 2nd data set in reference to the other (with the adjusted 3dWarp as you suggested), how would I go about to adding them in succession to a new 3d+t data set. After performing the adjusted 3dWarp, the data sets are now different matrix sizes. My ultimate goal is to adjust for the motion that happened between time point 1 and time point 2, and then add them together to look how the voxel signal changed between the time points. (i.e. so after 3dWarp, each voxel should be co-localized so I may look at the time course for each voxel) Thank you again for your help with this. I really appreciate it.

Cheers