[1] Massachusetts Gen Hosp, Dept Radiol, Athinoula A Martinos Ctr Biomed Imaging, Charlestown, MA 02129 USA
[2] Harvard Univ, Sch Med, Charlestown, MA 02129 USA
[3] Tech Univ Munich, Klinikum Rechts Isar, Nukl Med Klin & Poliklin, D-8000 Munich, Germany
[4] Max Planck Inst Neurol Res, D-50931 Cologne, Germany