1. Faculty of Health Sciences, Hokkaido University, Kita-12, Nishi-5, Kita-ku, Sapporo, Japan
2. Department of Health Sciences, School of Medicine, Hokkaido University, Kita-12, Nishi-5, Kita-ku, Sapporo, Japan
3. Diagnostic Center for Sonography, Hokkaido University Hospital, Kita-14, Nishi-5, Kita-ku, Sapporo, Japan
4. Department of Cardiovascular Medicine, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Kita-15, Nishi-7, Kita-ku, Sapporo, Japan