1 Department of Radiology, Stanford University School of Medicine, Stanford, CA; Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA. Electronic address: mastro@stanford.edu.
2 Department of Radiology, Stanford University School of Medicine, Stanford, CA.
3 University of California San Diego, Department of Radiology, La Jolla, CA.
4 Department of Radiology, Stanford University School of Medicine, Stanford, CA; Department of Radiology, University of Pennsylvania, Philadelphia, PA.