1. Department of Nuclear Medicine Peking University First Hospital 100034 Beijing P. R. China
2. State Key Laboratory of Organic-Inorganic Composites and Beijing Key Lab of Bioprocess Beijing University of Chemical Technology 15 Beisanhuan East Road, Chaoyang District 100029 Beijing P. R. China
3. Institute of Medical Technology Peking University 100871 Beijing P. R. China
4. Russell H. Morgan Department of Radiology The Johns Hopkins University School of Medicine Baltimore Maryland 21205 USA
5. F.M. Kirby Research Center for Functional Brain Imaging Kennedy Krieger Institute Baltimore Maryland 21205 USA
6. Department of Chemical and Biomolecular Engineering Johns Hopkins University Baltimore Maryland 21218 USA
7. Department of Radiology The First Affiliated Hospital of Jinan University 510632 Guangzhou, Guandong P. R. China