1Biomedical engineering, University of Alberta, Edmonton, AB, Canada, 2Medical Imaging, 2nd Affiliated Hospital of Shantou University Medical College, Shantou, China, People's Republic of, 3Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, MGH and Harvard Medical School, Charlestown, MA, United States, 4Math and Information Technology, Hanshan Normal University, Chaozhou, China, People's Republic of, 5Provincial key laboratory of medical molecular imaging, Shantou, China, People's Republic of