I'm working with PET data and SPM2 (I'm using SPM2 due to a compatibility problem in SPM5…).

I have water data and carbon tracer data. I want to realign the carbon tracer data to the water data.
When I do Realign I choose the water pic first, then my carbon tracer pic.

The question is: should I choose coreg&reslice or coreg only? Would it make any difference?

Next, after Realign, I want to Normalize using the SPM-provided PET.mnc as template, source water pic and image to write carbon tracer pic; and Smooth.

How does my choice of coreg with or without reslice affect my later steps in the preprocessing? Any other tips on how to handle my data set? Should I maybe choose Coregister the water and carbon pics instead of Realign?