Computed tomography (CT) image of the thorax of a brachycephalic dog at the level of the middle section of the ninth rib. The internal diameter of the right caudal bronchial lumen and diameter of the corresponding pulmonary artery in the cross-section were measured to determine the BA ratio. An arrow indicates the measured bronchus in the right caudal lung lobe while an arrowhead indicates the corresponding pulmonary artery.