1. Department of Medicine (R.K.), McGill University Health Center, McGill University, Montréal, Québec, Canada H3H 2R9
2. Department of Radiology (P.P.C., V.G.), Childrens Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California 90027
3. U.S. Department of Agriculture (T.R.), National Animal Disease Center, Ames, Iowa 50010