1. 1Department of Medicine I, Klinikum Vest, Knappschaftskrankenhaus Recklinghausen, Academic Teaching Hospital, Ruhr-University Bochum, Recklinghausen, Germany
2. 2Department of Nuclear Medicine, University Hospital Essen, Essen, Germany
3. 3Department of Endocrinology, Diabetes and Metabolism, Clinical Chemistry – Division of Laboratory Research; Endocrine Tumor Center at WTZ/Comprehensive Cancer Center, University Hospital Essen, University of Duisburg-Essen, Essen, Germany