1. Laboratory of Veterinary Radiology and Radiation Biology, Kitasato University School of Veterinary Medicine and Animal Sciences, Towada, Aomori 034-8628, Japan
2. Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan
3. Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo 185-8601, Japan