A three-dimensional volume data record contains a vascular tree. A two-dimensional projection image is an image of an actual fill state, to which the vascular tree is filled with a contrast agent at an acquisition time. The volume data record and the projection image are registered in relation to one another by means of the set of imaging parameters. A computation facility determines an expected target fill state, which describes which parts of the vascular tree should be filled with contrast agent at acquisition time in the three-dimensional volume data record. The computation facility determines the set of imaging parameters based on the target fill state and the projection image.