1 Department of Radiology, Kansai Medical University, 2-5-1 Shin-machi, Hirakata-shi, Osaka, 573-1010, Japan.
2 Medical Physics Laboratory, Division of Health Science, Graduate School of Medicine, Osaka University, 1-7 Yamadaoka, Suita-shi, Osaka. 565-0871, Japan.
3 Department of Advanced Medical Physics, Graduate School of Medicine, Kyoto University, 53 Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.