The present invention relates to a data processing method for providing variation data which describe a physically-varying anatomical structure, in particular an indiscernible anatomical structure, in particular a non-enhancing tumour, comprising the steps of: providing second image data which describe a second image of a region of an anatomical body, wherein the region includes a second anatomical part which includes the physically-varying anatomical structure； providing first image data which represent a first image of the same region, wherein said same region includes a first anatomical part which does not include the physically-varying anatomical structure or which includes the physically-varying anatomical structure in a different physical state than in the second anatomical part； providing position change data which describe positional changes of corresponding image elements between the first image and the second image, on the basis of the first and second image data； and providing the variation data on the basis of the position change data.
