1. Department of Radiology , School of Medicine, , S1W16, Chuo-ku, Sapporo, Hokkaido 060-8543 , Japan
2. Sapporo Medical University , School of Medicine, , S1W16, Chuo-ku, Sapporo, Hokkaido 060-8543 , Japan
3. Department of Biological Sciences , College of Sciences, , Bunkyo 2-1-1, Mito, Ibaraki 310-8512 , Japan
4. Ibaraki University , College of Sciences, , Bunkyo 2-1-1, Mito, Ibaraki 310-8512 , Japan
5. Department of Biological Sciences , Faculty of Sciences, , Bunkyo 2-1-1, Mito, Ibaraki 310-8512 , Japan
6. Ibaraki University , Faculty of Sciences, , Bunkyo 2-1-1, Mito, Ibaraki 310-8512 , Japan