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Pulmonary Embolism: Radiation Dose with Multi–Detector Row CT and Digital Angiography for Diagnosis¹

¹ From the Departments of Medical Imaging (E.C.) and Radiation Therapy (S.V., M.O.), Cliniques Universitaires St-Luc, Université Catholique de Louvain, Avenue Hippocrate, 10, 1200 Brussels, Belgium. Received April 7, 2005; revision requested June 7; revision received August 12; accepted September 13; final version accepted November 23. Address correspondence to E.C. (e-mail: coche{at}rdgn.ucl.ac.be).

Purpose: To compare radiation dose delivered at four– and 16–detector row computed tomography (CT) with a dose-modulation program and that delivered at digital angiography for evaluation of pulmonary embolism (PE).

Materials and Methods: The part of the study involving patients (seven women, four men; mean age, 62 years ± 16 [standard deviation]; range, 41–85 years) was approved by the institutional review board. Patients gave written informed consent. Exposure was performed with an anthropomorphic phantom with thermoluminescent dosimeters for four–detector row CT without the dose-modulation program and 16–detector row CT without and with the dose-modulation program with standard protocols for pulmonary CT angiography (120 kV, 144 mAs, four and 16 detector rows with 1.00- and 0.75-mm section thickness, respectively). Digital angiograms were acquired with four standard projections at 80 kV. For digital angiography, radiation dose was calculated according to phantom measurements and adapted to acquisition and fluoroscopy times. Distribution of dose was compared for CT and digital angiography.

Results: During pulmonary CT angiography, mean radiation dose delivered at middle of chest was 21.5, 19.5, and 18.2 mGy for four–detector row CT and for 16–detector row CT without and with dose-modulation program, respectively. At the same level, a mean dose of 91 mGy was delivered with digital angiography. The dose adjusted to clinical conditions was 139.0 mGy for digital angiography and could be reduced after technical adjustment. Ratios of maximum dose to mean dose were 1.15 and 2.96 for CT and digital angiography, respectively. With application of the dose-modulation program at 16–detector row CT, radiation dose was reduced 15%–20% at the upper chest.

Conclusion: Multi–detector row CT delivers a lower radiation dose, with better spatial distribution of dose, than does pulmonary CT angiography. With 16–detector row CT and a dose-modulation program, radiation dose is decreased during PE work-up.

© RSNA, 2006