"The cardiothoracic ratio is measured on a PA chest x-ray, and is the ratio of maximal horizontal cardiac diameter to maximal horizontal thoracic diameter (inner edge of ribs/edge of pleura)."
"The cardiothoracic ratio should not be measured on an AP chest x-ray. Objects nearer the x-ray tube appear artificially enlarged due to divergence of the x-ray beam, resulting in the heart appearing artificially large on AP radiographs."
"The cardiothoracic ratio should not be measured on an AP chest x-ray. Objects nearer the x-ray tube appear artificially enlarged due to divergence of the x-ray beam, resulting in the heart appearing artificially large on AP radiographs."
"In the following situations, cardiothoracic ratio is more than 0.5 on a PA chest radiograph, but heart and pericardium are normal:"
Expected headings
"Related pathology"