By David Sutton, MD, FRCP, FRCR, DMRD, MCAR(Hon) MD MD, Consulting Radiologist, St. Mary's Hospital; Consulting Radiologist, National Hospital for Neurology and Neurosurgery, London, UK University of Virginia Health Sciences Center, Charlottesville, VA Assistant Professor, Tufts University School of Medicine and Attending Physician, Divisions of Geographic Medicine and Infectious Diseases, New England Medical Center, Department of Medicine, Lemual Shattuck Hospital, Boston, MA