[1] Univ Milano Bicocca, Viale Sarca 336, I-20149 Milan, Italy
[2] Peking Univ, Room 1431,Sci Bldg 1, Beijing 100871, Peoples R China
[3] Siemens Healthcare Diagnost, 1584 Enterprise Blvd W, Sacramento, CA 95691 USA
[4] Oxford Brookes Univ, Oxford OX33 1HX, England