1. A labeling apparatus for labeling structures of an object shown in an object image, the labeling apparatus comprising: a contour providing unit for providing a contour representing a structure in the object image, a probability map providing unit for providing a probability map, the probability map indicating for different labels, which are indicative of different structures of the object, and for different positions in the probability map the probability that the respective structure, which is indicated by the respective label, is present at the respective position, wherein the probability depends on the position in the probability map, a mapping unit for mapping the probability map to the object image such that the positions in the probability map are assigned to positions in the object image, and a label assigning unit for assigning to the contour label based on the mapped probability map, the label assigning unit being adapted to define positions of image elements in accordance with the provided contour and with a predefined definition rule, the predefined definition rule defining positions of image elements depending on a contour, determine for each label a label probability depending on the probabilities which are defined by the mapped probability map and the defined positions of image elements, and assign the label to the contour for which the largest label probability has been determined