Statistical analysis for different size images

Hi there, I’m trying to do 3dttest on my database, and I haven’t done any registration because I wanted to stay in the original space.
I know that t-test is a voxelwise analysis, but I don’t want to lose original space.
Do you have any idea what I can do?

Could you provide more information about the input files you’re trying to feed into 3dttest++? What kind of data are those input files?