Method to bring out a temporal difference between corresponding structures in a reference image R and a floating image F by convolving the reference image R and the floating image F with a window function H.sub.w to generate R.sub.w and F.sub.w, applying a non-rigid transformation resulting in a transformation field g(r.sub.R) mapping every location r.sub.R to a corresponding location r.sub.F in the floating image F and generating a subtraction image by performing subtraction R.sub.w(r)-F.sub.w(g(r)) wherein r represents a voxel (x, y, z) in reference image R.