aDepartment of Gastroenterology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan

bDepartment of Endoscopy and Endoscopic Surgery, The University of Tokyo Hospital, Tokyo, Japan

Correspondence to Yousuke Nakai, MD, PhD, Department of Endoscopy and Endoscopic Surgery, The University of Tokyo Hospital, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. Tel: +81 3 3815 5411; fax: +81 3 3814 0021; e-mail: [email protected]