2-D projection images show the temporal profile of the distribution of a contrast medium in an examination object, which contains a vascular system and its surroundings. Each projection image comprises pixels with pixel values. The pixel values of pixels corresponding to one another in the projection images are defined by at least essentially locationally identical areas of the examination object. A computer assigns a uniform 2-D evaluation core that is uniform for all corresponding pixels at least in a sub-area of pixels corresponding to one another in the projection images that is uniform for the projection images. The computer defines at least one characteristic value for each pixel within each projection image based on the evaluation core assigned to the pixel and assigns it to the relevant pixel. Based on the temporal profile of the characteristic values, the computer defines parameters of at least one function of time, so that any deviation between the function parameterized with the parameters and the temporal profile of the characteristic values is minimized. Based on the parameters the computer defines a type and/or an extent and assigns them to a pixel of a 2-D evaluation image corresponding to the pixels of the projection images. The type indicates whether the respective pixel of the evaluation image corresponds to a vessel of the vascular system, a perfused part or a non-perfused part of the surroundings of a vessel of the vascular system. The extent is characteristic of perfusion. The computer outputs at least the sub-area of the evaluation image to a user via a display device.