Arterial-phase postcontrast transverse thoracic angiogram CT image at the level of the pulmonary trunk (PT) in a 16 kg male beagle with an RPAD index of 17%. The PT to aorta ratio measurement technique consists of the measure of the maximum diameter of the PT measured immediately ventral to the bifurcation into left and right pulmonary arteries (solid line) and the measure of the short axis of the diameter of the descending part of the aorta (DAo) (solid line double arrow) or the short axis of the diameter of the ascending part of the aorta (AAo) (no solid line double arrow). The PT:DAo ratio of this dog was 1.72 and the PT:AAo ratio was 1.47.