I need to calculate the correlation between two 3D volumes. I've tried implementing Pearson's coefficient since it's well recognised in the literature but it only seems to spit out meaningless answers (see code snippet below):
A = volume1 - mean(volume1, 'all');
B = volume2 - mean(volume2, 'all');
num = sum(A .* B, 'all');
den1 = sum(A.^2, 'all');
den2 = sum(B.^2, 'all');
r = num ./ (den1 .* den2)^0.5;
Is there something I'm doing wrong here? What alternative correlations metrics might work in this context?