1. Department of Radiology, Massachusetts General Hospital, Boston, MA 02114, USA
2. Harvard Medical School, Harvard University, Boston, MA 02115, USA
3. Department of Surgery, Massachusetts General Hospital, Boston, MA 02114, USA
4. Department of Gastroenterology, Massachusetts General Hospital, Boston, MA 02114, USA
5. Sahlgrenska University Hospital, University of Gothenburg, 413 45 Gothenburg, Sweden
6. Department of Surgery, Mbarara University of Science and Technology, Mbarara P.O. Box 1410, Uganda
7. School of Medicine, Uganda Christian University, Mukono P.O. Box 4, Uganda