title: The O-sign.
authors: Nicholas
authors: N
authors: Eastley
authors: Mark
authors: M
authors: Turner
authors: Michael
authors: M
authors: Darby
mesh_terms: D016477:Artifacts; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008875:Middle Aged; D011027:Pneumoperitoneum / Q000000981:diagnostic imaging*; D011030:Pneumothorax / Q000000981:diagnostic imaging*; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging*; D012134:Respiratory Protective Devices; D035441:Thoracic Wall / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed