1Funktionelle Bildgebung, Deutsches Primatenzentrum, Göttingen, Germany, 2Molecular Imaging North Competence Center, University Medical Center Schleswig-Holstein, Kiel, Germany, 3Department of Physics, Christian-Albrechts-University, Kiel, Germany, 4Department for Nephrology and Hypertension, University Medical Center Schleswig-Holstein, Kiel, Germany