1. University of Florida, Department of Neurosurgery, P.O. Box 100265, Gainesville, FL 32610-0265, USA
2. Assiut University, Department of Radiology, Assiut 71515, Egypt
3. University of Florida, College of Medicine, Gainesville, FL 32603, USA
4. Division of Interventional Neuroradiology, Abbott Northwestern Hospital, Minneapolis, MN 55407, USA