1. Department of Radiology, University of Tsukuba Hospital, Tsukuba, Ibaraki, Japan
2. Department of Radiology, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan
3. Department of Radiology Technology, University of Tsukuba Hospital, Tsukuba, Ibaraki, Japan
4. Department of Obstetrics and Gynecology, Institute of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan