Measurement of intragastric pressure: an objective method to ascertain whether gastric wall extension is sufficient for assessment of the non-extension sign* oleh Kentaro Imamura, Motoko Machii, Kenshi Yao, Suketo Sou, Takashi Nagahama, Tsuneyoshi Yao, Takao Kanemitsu, Masaki Miyaoka, Kensei Ohtsu, Toshiharu Ueki