[1] Univ Hosp Ulm, Dept Diagnost & Intervent Radiol, Albert Einstein Allee 23, D-89081 Ulm, Germany
[2] Tech Univ Munich, Klinikum Rechts Isar, Sch Med, Dept Diagnost & Intervent Neuroradiol, Ismaninger Str 22, D-81675 Munich, Germany
[3] Tech Univ Munich, Klinikum Rechts Isar, TUM Neuroimaging Ctr, D-81675 Munich, Germany
[4] Kuopio Univ Hosp, Dept Clin Neurophysiol, POB 100, Kys Kuopio 70029, Finland
[5] Univ Eastern Finland, Dept Appl Phys, Kuopio 70210, Finland