1. Department of Radiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan,
2. Department of Radiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan
3. Boya farm, Hokkaido, Japan, Laboratory of Animal Reproduction, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan
4. Laboratory of Animal Reproduction, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan