A new traction device for facilitating endoscopic submucosal dissection (ESD) for early gastric cancer: the “medical ring” - Matsumoto, K.; Nagahara, A.; Sakamoto, N.; Suyama, M.; Konuma, H.; Morimoto, T.; Sagawa, E.; Ueyama, H.; Takahashi, T.; Beppu, K.; Shibuya, T.; Osada, T.; Yoshizawa, T.; Ogihara, T.; Watanabe, S. (Endoscopy, 2011)