1. Faculty of Medicine, Gadarif University, Gadarif, Sudan
2. King Abdu Aziz Armed Forces Hospital at Air Base, Dhahran, Kingdom of Saudi Arabia
3. Unaizah College of Medicine, Qassim University, Unaizah, Kingdom of Saudi Arabia
4. Faculty of Medicine, University of Khartoum, P.O. Box 102, Khartoum, Sudan