Use of expiratory CT pulmonary angiography to reduce inspiration and breath-hold associated artefact: contrast dynamics and implications for scan protocol.

Objective: To investigate the effects of scanning in expiration during computed tomography pulmonary angiography (CTPA).

Methods: One hundred and eighty-one consecutive expiratory CTPA examinations were compared with 145 inspiratory CTPA examinations performed using a standardized protocol through assessment of attenuation seen in the cardiac chambers, pulmonary artery (PA), and ascending aorta.

Results: Expiratory scans showed greater attenuation at the pulmonary trunk, right PA, left PA, lobar and segmental PAs (p<0.05). Expiratory scans showed a lower incidence of transient contrast medium interruption (p<0.001) and generalized unsatisfactory PA opacification (p<0.05). Scans with generalized low PA attenuation had lower attenuation in the right ventricle, left heart, and ascending aorta (p<0.001) suggesting that contrast medium delivery or dilution prior to contrast medium entry into the PA is responsible. Expiratory scans showed lower quality scores (p<0.001) for depiction of lung parenchyma.

Conclusions: Expiratory scanning could be used as an optimal protocol for dedicated PA imaging. However, it suffers from inferior parenchymal imaging and should probably be reserved for failed inspiratory breath-hold CTPA.