1. Center for Biomedical Imaging Research; Department of Biomedical Engineering; School of Medicine; Tsinghua University; Beijing 100084 China
2. Department of Radiology; Beijing Anzhen Hospital; Capital Medical University; Beijing 100029 China
3. Clinical Sites Research Program; Philips Research North America; Briarcliff Manor NY 10510 USA
4. Department of Radiology; University of Washington; Seattle WA 98109 USA