Respiratory phase can affect pulmonary vein-to-pulmonary artery ratio measured with CT.

Objective: To evaluate pulmonary vein (PV)-to-pulmonary artery (PA) ratios obtained in healthy dogs by means of various CT protocols, accounting for the effects of the respiratory phase and contrast agent used.

Animals: 10 healthy Beagles.

Procedures: Before and after contrast medium (600 mg iodine/kg) was injected IV, thoracic CT was performed with a positive-pressure breath-hold (inspiratory phase) and at the end of expiration (expiratory phase). After CT scanning, echocardiography was performed, and an optimized right parasternal long-axis view was obtained for measurement of PV and PA diameters. The PV and PA diameters were measured subsequently for each CT protocol.

Results: Mean ± SD PV:PA values obtained from pre- and postcontrast inspiratory CT were 1.058 ± 0.072 and 1.020 ± 0.053, respectively, which were comparable to the echocardiographic value (P > .05). Mean PV:PA values obtained with pre- and postcontrast expiratory CT were 1.259 ± 0.094 and 1.239 ± 0.066, respectively, which were significantly (P = .005) greater than inspiratory CT measurements. There was a significant (r > 0.5, P < .05) linear relationship between PV:PA values obtained with pre- and postcontrast inspiratory CT and echocardiography.

Clinical Relevance: PV:PA could be measured with thoracic CT in a manner similar to that for echocardiography. However, PV:PA values measured with expiratory CT were different from previously reported values. Therefore, the respiratory phase should be considered when evaluating pulmonary vascular size through CT, and measurements with the inspiratory CT protocol would be more accurate.