The prone chest film.
Frontal chest radiographs in the prone position enhanced visualization of the posterior lung base in the presence of pleural effusions. Though the lateral decubitus view often displaced fluid adequately, in several cases only the prone film revealed basilar lung pathology; this was due to gravitational shift of the fluid away from this region as well as improved aeration of the lower lobe in the prone position, as shown by horizontal-beam  lateral views. The prone chest film is recommended for evaluation of the lung base when obscured by fluid.
D000009:Abdominal Muscles / Q000033:anatomy & histology; D001995:Bronchography; D003964:Diaphragm / Q000033:anatomy & histology; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging*; D008482:Mediastinum / Q000033:anatomy & histology; D010996:Pleural Effusion / Q000000981:diagnostic imaging*; D011187:Posture; D011651:Pulmonary Artery / Q000033:anatomy & histology; D011652:Pulmonary Circulation; D011667:Pulmonary Veins / Q000033:anatomy & histology; D013270:Stomach / Q000033:anatomy & histology