An automatic computer implemented technique which may be used for identifying markers and determining the centroids of fiducial markers (e.g., cylindrical fiducial markers) attached to the head in magnetic resonance (MR) and X-ray computed tomography (CT) volume images is disclosed....http://www.google.de/patents/US5769789?utm_source=gb-gplus-sharePatent US5769789 - Automatic technique for localizing externally attached fiducial markers in volume images of the head 
