1. Institute of Molecular Bioimaging and Physiology, National Research Council (IBFM-CNR), Cefalù, Italy
2. National Institute for Nuclear Physics, Laboratori Nazionali del Sud, INFN-LNS, Catania, Italy
3. Department of Physics and Astronomy, University of Catania, Catania, Italy
4. Department of Physics, University of Naples Federico II, via Cintia, I-80126 Naples, Italy
5. Department of Health Sciences, Tecnomed Foundation, University of Milano-Bicocca, Milan, Italy