1. From the Department of Diagnostic and Interventional Neuroradiology (G.B., F.F., A.S., T.D.F., U.H., H.L., J.F., S.G., A.K.)
2. Institute of Medical Biometry and Epidemiology (A.A.), University Medical Center Hamburg-Eppendorf, Germany
3. Department of Radiology, Friedrich-Ebert-Hospital Neumuenster, Germany (S.I.B.)
4. Department of Neuroradiology, University Hospital Schleswig-Holstein, Luebeck, Germany (A.K.)
5. Department of Radiology, University Hospital Muenster, Germany (A.K.).