1. A method 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, the method comprising: provisioning image data of the examination region with the aid of imaging diagnostic medical equipment; selecting at least one section of a reference vessel permeated by contrast agent from the blood vessel system illustrated in the provisioned image data; and normalizing the provisioned image data with respect to the contrast on the basis of image data from the selected at least one section of the reference vessel.