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Chest Imaging

E2638. Time Is of the Essence in CT Pulmonary Angiography: Benefits of Empiric Timing

Hsu K,  Levsky J,  Haramati L,  Gohari A. Montefiore Medical Center, Bronx, NY

Address correspondence to K. Hsu (

Objective: We instituted a new, simple CT pulmonary angiography (CTPA) contrast 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 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 vs 359 HU, p < 0.001) and aorta (381 vs 218 HU, p < 0.01) in the empiric timing group versus the timing bolus group, respectively. Radiation exposure was significantly lower (5.3 vs 6.0 mSv, p = 0.05) in the empiric timing group, despite a higher body mass index (31 vs 29 kg/m2, p < 0.01). Pulmonary embolism positivity rate was not significantly higher in the timing bolus versus the empiric timing group (19% vs 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.