1 From the Departments of Radiology (R.R.E.) and Medicine (A.P.), NorthShore University HealthSystem, 2650 Ridge Ave, Walgreen Bldg, G534, Evanston, IL 60201; Feinberg School of Medicine, Northwestern University, Chicago, Ill (R.R.E.); and Pritzker School of Medicine, University of Chicago, Chicago, Ill (A.P.).