1Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China, People's Republic of, 2Department of Radiology, The Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, China, People's Republic of, 3Vascular Imaging Laboratory, Department of Radiology, University of Washington, Seattle, WA, United States