1Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyamacho, Toyonaka, Osaka 560-8531, Japan
2Department of Neurosurgery, Nagoya City University Graduate School of Medical Science, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya, Aichi 467-8601, Japan
3Interfaculty Initiative in Information Studies / Institute of Industrial Science, The University of Tokyo, Tokyo, Japan
4Department of Neurosurgery, Shiga University of Medical Science, Setatsukinowacho, Otsu, Shiga 520-2192, Japan
5Department of Radiology, Shiga University of Medical Science, Setatsukinowacho, Otsu, Shiga 520-2192, Japan