1. A method for determining a three-dimensional model dataset of a blood vessel system of a patient including at least one vessel segment from a number of projection images of the blood vessel system, the projection images recorded from different recording angles, the method comprising: dividing the projection images up into image areas each containing at least one pixel, determining a feature vector comprising at least image data of at least the image area and/or computation data computed as a function of the image data, for each of the image areas, defining classification information that describes how the respective image area belongs to a vessel segment of the blood vessel system defined in accordance with anatomical specification data or describes how the respective image area does not belong to the blood vessel system, for each of the image areas, the defining being by applying a classification function to the feature vector assigned to the image area, wherein the classification function has been trained by training data records annotated with classification information obtained from at least one person other than the patient, segmenting the blood vessel system in the projection images by grouping image areas with the same classification information, and calculating the three-dimensional model dataset as a function of the segmented projection images and the classification information.