1. Department of Neurosurgery Tsukuba Medical Center Hospital, Tsukuba, Japan.
2. Department of Radiology, Tsukuba Medical Center Hospital, Tsukuba, Japan.
3. Department of Neurosurgery Faculty of Medicine, University of Tsukuba, Tsukuba, Japan.
4. Department of Stroke, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan.