1. Department of Radiology and Diagnostic Imaging, University of Alberta, 2B2.41 WMC, 8440-112 St NW, Edmonton, AB T6G 2B7, Canada
2. Evidence-Based Practice Center, Mayo Clinic, Rochester, MN
3. Departments of Radiology and Epidemiology, University of Ottawa, Ottawa Hospital Research Institute, Ottawa, ON, Canada
4. Department of Neurosurgery, University of California, San Francisco, CA
5. Department of Surgery, Division of Neurosurgery, University of Alberta, Edmonton, AB, Canada