1 Department of Radiology, Saitama Medical Center, Jichi Medical University, 1-847 Amanuma-Cho, Omiya-Ku, Saitama-shi, Saitama-Ken, 330-8503, Japan. omanabe@jichi.ac.jp.
2 Department of Cardiovascular Medicine, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, Japan.