1. Division of Gastroenterology, Department of Internal Medicine, Korea University Guro Hospital, Korea University College of Medicine, Seoul 08308, Republic of Korea
2. Division of Gastroenterology and Hepatology, Department of Internal Medicine, Institute of Gastrointestinal Medical Instrument Research, Korea University College of Medicine, Seoul 02841, Republic of Korea
3. Department of Internal Medicine, Korea University Ansan Hospital, Ansan, Gyeonggi 15355, Republic of Korea