1 Department of Radiology and Biomedical Imaging, University of California-San Francisco, 505 Parnassus Avenue, M391, Box 0628, San Francisco, CA 94143-0628, USA. Electronic address: Benjamin.Yeh@ucsf.edu.
2 Department of Radiology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, 676 North Saint Clair Suite 800, Chicago, IL 60611, USA. Electronic address: Frank.Miller@nm.org.