Performance of a simple robust empiric timing protocol for CT pulmonary angiography

Objective We instituted a new, simple CT pulmonary angiography (CTPA) contrast material timing protocol using a standard empiric delay to replace our previous timing bolus method. This study tests the hypothesis that the empiric protocol more consistently produces diagnostic quality images of both the pulmonary arteries and the aorta with lower radiation exposure. Materials and methods We performed a retrospective review of consecutive CTPAs for 2 months both before and after the protocol change. Pulmonary artery and aortic enhancement, patient characteristics, radiation exposure and results of CTPA were analyzed. Results There were 182 patients in the timing bolus group and 164 in the empiric timing group. Both groups had a female majority (59%) and a similar mean age (58 and 57 years, respectively). Enhancement was significantly higher both for the pulmonary artery (median 400 HU versus 359 HU, P < 0.001) and aorta (median 381 HU versus 218 HU, P < 0.01) in the empiric timing group versus the timing bolus group, respectively. Radiation exposure was lower (5.3 mSv versus 6.0 mSv, P = 0.05) in the empiric timing group, despite a higher body-mass-index (31 versus 29 kg/m², P < 0.01). Pulmonary embolism positivity rate was non-significantly higher in the timing bolus vs the empiric timing group (19% and 13%, P = 0.1). Conclusion A simple empiric timing protocol for CTPA has robust performance compared to a timing bolus protocol. Empiric timing preserves the required high diagnostic quality for evaluation of the pulmonary arteries with the added benefits of aortic enhancement and lower radiation exposure.