1. Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany, Department of Neurology, Klinikum rechts der Isar, Technische Universität München, Möhlstrasse 28, D-81675 Munich, Germany, ABX Advanced Biochemical Compounds GmbH, Heinrich-Glaeser-Strasse 10-14, D-01454 Radeberg, Germany, and Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli “Federico II”, Via D. Montesano, 49-80131 Napoli, Italy