1. HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital , FI-00290 Helsinki, Finland
2. Department of Physics, University of Helsinki , FI-00014 Helsinki, Finland
3. Suomen Terveystalo Ltd , Jaakonkatu 3A, FI-00100 Helsinki, Finland
4. STUK-Radiation and Nuclear Safety Authority , Jokiniemenkuja 1, FI-01370 Vantaa, Finland