1 Department of Radiology, Brooke Army Medical Center, Fort Sam Houston, 3551 Roger Brooke Dr, San Antonio, TX 78234. 2 Department of Radiology, Uniformed Services University, Bethesda, MD. 3 Department of Medical Imaging, University of Arizona, Tucson, AZ. 4 Departments of Medicine and Biomedical Engineering, University of Arizona, Tucson, AZ.