A novel biliary cannulation method for difficult cannulation cases using a unique, uneven, double-lumen cannula (Uneven method) - Takenaka, Mamoru; Arisaka, Yoshifumi; Sakai, Arata; Kobayashi, Takashi; Shiomi, Hideyuki; Masuda, Atshuhiro; Kudo, Masatoshi (Endoscopy, 2018)