1. Department of Gastroenterological Surgery, Kochi Health Sciences Center, Kochi, Japan
2. Department of Gastroenterology and Hepatology, Kochi Health Sciences Center, Kochi, Japan
3. Department of Radiology, Kochi Health Sciences Center, Kochi, Japan
4. Department of Diagnostic Pathology, Kochi Health Sciences Center, Kochi, Japan
5. Department of Biostatistics, National Center for Global Health and Medicine, Shinjuku, Japan