The invention relates to the analysis of successive data sets. A local intensity variation is formed from such successive data sets, that is, from data values in successive data sets at corresponding positions in each of the data sets. A region of interest is localized in the individual data sets on the basis of the local intensity variation. In particular the time derivative of the local intensity variation is used to localize the region of interest. The invention can be used notably for cardiological applications so as to separate the image of the myocardium from a sequence of 3D magnetic resonance reconstruction images.