[1] Univ Toronto, Toronto Western Hosp, Dept Med Imaging, Div Neuroradiol, Toronto, ON M5T 2S8, Canada
[2] Univ Calgary, Foothills Med Ctr, Dept Med Imaging, Div Neuroradiol, Calgary, AB, Canada
[3] Univ Toronto, St Michaels Hosp, Dept Med Imaging, Div Neuroradiol, Toronto, ON M5B 1W8, Canada
[4] Univ Toronto, Univ Hlth Network, Dept Med, Toronto, ON, Canada