I’ve been trying to find a way to get a map of the difference between two independent CTh association maps but can’t seem to find a solution.

I have two maps of independent groups (one is N=15, the other N=20) I would like to compare. Is there maybe a way to do a sig1.mgh – sig2.mgh and then visualize this? Not sure how to go about it. I’m basically trying to visualize what is left over after subtracting one map from the other (independent samples t-test of sorts).