A method and a correspondingly configured tomography scanner are disclosed for normalizing image data with respect to a contrast in the image data produced by a contrast agent, the image data illustrating a tissue structure to be examined and at least part of a blood vessel system of an examination region connected to the tissue structure, which are at least in part permeated by the contrast agent. In an embodiment of the method, image data of the examination region is provided with the aid of the tomography scanner. At least one section of a reference vessel permeated by contrast agent is selected in the image data. The image data is normalized on the basis of image data from the section of the reference vessel such that the contrast in the image data as a result of the contrast agent is almost independent of patient-specific and examination-specific parameters in order to ensure that image data from different times can be compared.