Enhancement of the pulmonary arteries and thoracic aorta: comparison of a biphasic contrast injection and fixed delay protocol with a monophasic injection and a timing bolus protocol.

The definitive diagnosis of pulmonary embolism, a significant cause of morbidity and mortality, relies on imaging. In this study, we compare the conventional computed tomography pulmonary angiogram (CTPA) protocol to a double-rule out CT angiogram (DRO CTA) protocol in terms of vascular enhancement, radiation dose, and contrast volume delivered. The CTPA protocol involves injection of a timing bolus for localization of the pulmonary artery, whereas the DRO CTA protocol involves a biphasic contrast. We analyzed 248 consecutive CTPA studies and 242 consecutive DRO CTA studies. Vessel enhancement using region of interest (ROI) measurements, radiation dose delivered, and total contrast volume administered was recorded. The enhancement of all vessels measured was statistically significantly higher with the biphasic DRO CTA protocol than the CTPA protocol. The difference in mean vascular enhancement for the two protocols was greatest in the descending aorta (DA, P < 0.001) and least in the main pulmonary artery (MPA, P = 0.001). The percent of studies with vascular enhancement ≥250 Hounsfield units (HU) was significantly greater in all vascular beds except the MPA when the DRO CTA protocol was used. Studies performed with the DRO CTA protocol led to less radiation exposure and used less contrast than those performed with the CTPA protocol (P < 0.001 for both). According to the final radiology report, 35.08 % of studies in the CTPA group and 22.31 % of studies in the DRO CTA group were considered indeterminate (P = 0.001). In conclusion, the biphasic DRO CTA protocol leads to statistically significantly higher opacification of all pulmonary arterial and aortic vessels studied, with no greater delivery of radiation or contrast, than the monophasic CTPA protocol.