1. A method for obtaining registration of a three-dimensional pre-operative image data set of an anatomical vessel tree with corresponding intra-operative image data reconstructed from two-dimensional images of the vessel tree obtained in an X-ray imaging system, comprising: determining the orientation direction of a vessel from a three-dimensional pre-operative image data set, and determining the orientation direction of the vessel from the X-ray image planes by identifying on at least two X-ray images at least two X-ray image data points on the vessel that provide a linear indication of the local direction of the vessel in the X-ray image planes, from which an orientation direction of the vessel is defined, and determining a transformation of the three-dimensional image data to obtain a best fit registration of the direction derived from the pre-operative image data set with the direction derived from the X-ray image data points.