1. An image evaluation method for a two-dimensional projection image of an examination object containing a vascular system and a surroundings thereof, comprising: displaying a temporal course of a distribution of a contrast medium in the examination object by the projection image having a plurality of pixels with pixel values defined by an area of the examination object; determining a two-dimensional evaluation image based on the projection image having a plurality of pixels corresponding to the pixels of the projection image via a computer and outputting the evaluation image to a user via a display device; determining a type for each of the pixels in a sub-area of the evaluation image and assigning the determined type to the pixel, the type: characteristic of whether the pixel corresponding to a vessel of the vascular system, a perfused part of the surroundings or a non-perfused part of the surroundings, determined from the temporal course of the pixel values of the pixels of the projection image which is in a two-dimensional type evaluation core defined by a respective pixel of the evaluation image; and determining an extent of a perfusion of a corresponding area of the examination object in the pixels of the evaluation image assigned the type of perfused part of the surroundings and assigning the extent to the respective pixel, the extent determined from the temporal course of the pixel values of the pixels of the projection image which is in a two-dimensional basic extent-evaluation core defined by a respective pixel of the evaluation image, wherein the computer: determines the extent in the pixels of the evaluation image assigned the type of perfused part of the surroundings and in the pixels surrounded within a predetermined minimum distance of the pixels assigned the type of perfused part of the surroundings, and assigns the extent from the temporal course of the pixel values of the pixels of the projection image which is in an additional extent-evaluation core contained in a corresponding basic extent-evaluation core of the projection image defined by a respective pixel of the evaluation image.