The invention relates to a method and an examination apparatus (10) for the observation of a catheter (43) in a vessel system. First, a 3D model of the vessel system is reconstructed with the help of differently oriented X-ray projections (Pi,...) generated by a C-arm system (20) during the injection of a contrast agent. Next, a movement corridor (M) of the catheter (43) is determined from the 3D model. During an examination procedure, current projections (P) are generated showing an image (43) of the catheter that can be registered with the reconstructed 3D model and/or the movement corridor (M). Based on the known current location (43") of the catheter in the 3D model of the vessel geometry or the movement corridor (M), an optimal projection direction (dopt) can be determined and assumed by the C-arm system (20) for the next projections to be generated.
