Image Acquisition

Multienergy CT pulmonary angiograms for both cohorts were acquired using the same multienergy protocol with one single-source Revolution CT scanner (GE Medical Systems). The acquisition rapidly switched kilovoltage peak (80 to 140 kVp), and data were acquired helically with an 80-mm detector width, median pitch of 1.38 (range, 0.98–1.38), and 0.5-second revolution time. Median tube current was 485 mAs (range, 240–630 mAs). Patients were administered iohexol contrast media (Omnipaque; GE Healthcare) with a concentration of 350 mg/mL based on BMI (BMI < 20: 60 mL at 4 mL/sec, BMI 20–29.9: 75 mL at 5 mL/sec, BMI 30–39.9: 80 mL at 5.5 mL/sec, BMI > 40: 90 mL at 6 mL/sec; median volume, 75 mL; range, 50–150 mL). Imaging was timed for pulmonary arterial phase imaging using SmartPrep bolus tracking software (GE Healthcare), with images acquired 8 seconds after main pulmonary artery enhancement at the T4 level reached 125 HU (19). Iodine-water material decompositions yielding iodine concentration in milligrams per milliliter were generated using the Gemstone Spectral Imaging software (GE Healthcare). All images were reconstructed on a 512 × 512 image grid with an xy resolution of 0.7 mm ± 0.1 (SD) (range, 0.5–0.9 mm) and section thickness of 1.25 mm. The typical field of view was 345 × 345 mm (range, 250–470 mm). Virtual monoenergetic images were reconstructed from the multienergy acquisition to simulate a 70 keV acquisition.