1. 5th Medical Department, Division of Endocrinology and Diabetes, Medical Faculty Mannheim, Heidelberg University , Mannheim 68167 , Germany
2. Department of Medicine I, Klinikum Vest, Knappschaftskrankenhaus Recklinghausen, Academic Teaching Hospital, Ruhr-University Bochum , Recklinghausen 45657 , Germany
3. Department 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 45147 , Germany
4. Department of Nuclear Medicine, University Hospital Essen, University of Duisburg-Essen , Essen 45147 , Germany