1. Department of Radiology, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
2. Department of Radiological Technology, Faculty of Medical Sciences, Kyoto College of Medical Science, Kyoto 622-0041, Japan
3. Department of Neurosurgery, Faculty of Medical Sciences, University of Fukui, Fukui 910-1193, Japan
4. Biomedical Imaging Research Center, University of Fukui, Fukui 910-1193, Japan