1. A method for determining a proportion of necrotic tissue in a defined tissue area of an object under examination based on a relatively high-energy image dataset including the tissue area of the object under examination and a relatively low-energy image dataset including the tissue area of the object under examination, the method comprising: determining a virtual contrast medium image based on the relatively high-energy image dataset and the relatively low-energy image dataset; segmenting the tissue area into a segmentation image dataset based on at least one of the relatively high-energy image dataset and the relatively low-energy image dataset, and producing a segmentation result; transmitting the segmentation result into the virtual contrast medium image and segmenting the tissue area in the virtual contrast medium image based upon the segmentation result; and executing an analysis of values of pixels belonging to the segmented tissue area of the virtual contrast medium image to determine the proportion of necrotic tissue in the defined tissue area by identifying pixels assignable to the necrotic tissue.