1Center for Biomedical Imaging Research, Department of Biomedical Enginnering, School of Medicine, Tsinghua University, Beijing, China, People's Republic of, 2Institute of nuclear and new energy technology, Tsinghua University, Beijing, China, People's Republic of, 3Radiology, Weill Cornell Medical College, New York, NY, United States, 4Healthcare Department, Philips Research China, Shanghai, China, People's Republic of, 5Biomedical Engineering, Cornell University, New York, NY, United States