Pulmonary trunk to aortic ratio

Last revised by Daniel J Bell on 21 Jul 2022

The pulmonary trunk to aortic ratio (PA:A), also known as main pulmonary artery to aorta ratio (MPA:A), is a measurement that can be made on CT and MRI scans and, in some instances on echocardiography 3. In most instances, a normal ratio in adults is taken 1:1 or less, and with ratios greater than that suggests:

However, some studies state that it can be normal up to 1.09:1 in the pediatric population (with some reports suggesting the cut off ratio in children being closer to 1.3:1 8).


It is usually measured on axial (ideally orthogonal) images just prior to the pulmonary artery bifurcation.


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