1. Faculty of Medicine, Sofia University “St. Kliment Ohridski”, 1 Koziak Str., Sofia 1407, Bulgaria
2. Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, 21 Acad. G. Bonchev Str., Sofia 1113, Bulgaria
3. Department of Molecular Imaging and Theranostics, National Institutes for Quantum and Radiological Science and Technology (QST/NIRS), 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan