1. A method for reinitializing a temporal sequence of fluoroscopic images of an examination region of an examination object, wherein the examination region comprises a vascular system including arteries and/or veins as blood vessels, comprising: assigning an acquisition time to each of the fluoroscopic images representing a given distribution of a substance in the examination region at the acquisition time; receiving the temporal sequence of the fluoroscopic images by a computer; determining an evaluation image based on differences from a mask image to be output to a user corresponding spatially on a pixel-by-pixel basis to the fluoroscopic images by the computer; calculating a differential value between a pixel of the evaluation image at a time t and a pixel at a preceding time t−1 by the computer, the differential value providing a metric for image change; determining a specific time t′ for reinitializing the mask image for the temporal sequence of the fluoroscopic images as a function of the differential value by the computer, wherein the specific time t′ corresponds with a time in which a minimal image change is present in the temporal sequence; and reinitializing the mask image for the temporal sequence of the fluoroscopic images at the specific time t′ by the computer.