1. STUK-Radiation and Nuclear Safety Authority, POB 14, Helsinki 00811, Finland
2. HUS Medical Imaging Center, Helsinki University Hospital, Helsinki, Finland
3. Department of Physics, University of Helsinki, Helsinki, Finland
4. HUS Medical Imaging Center, Clinical Physiology and Nuclear Medicine, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
5. OYS Department of Nuclear Medicine and Radiology, Oulu University Hospital, Oulu, Finland
6. Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland