1. University Medical Center Utrecht; Department of Radiology; Heidelberglaan 100 Utrecht Netherlands 3508 GA
2. University Medical Center Utrecht; Julius Centre for Health Sciences and Primary Care; PO Box 85500 Utrecht Netherlands 3508 GA
3. University Medical Center Utrecht; Department of Neurology; Heidelberglaan 100 Utrecht Netherlands 3508 GA
4. Radcliffe Infirmary; Neurovascular Research Unit; Oxford UK OX2 6HE
5. UK Cochrane Centre; National Institute for Health Research Summertown Pavilion, Middle Way Oxford UK OX2 7LG