(A) OCT image of normal squamous epithelium (bar = 500µm) shows a 5-layered appearance (from top to bottom: epithelium, lamina propria, muscularis mucosa, submucosa, and muscularis propria). (B) OCT image of gastric mucosa with “pit and crypt” architecture. (C) OCT image of BE with an irregular mucosal surface and absence of a layered or pit and crypt architecture. (D) OCT image of BE with submucosal glands (circled). (Figure and caption adapted from [121], with permission from Elsevier.)