Vascular attenuation and volumetric lung iodine density in dual-layer spectral CT pulmonary angiography: a randomized controlled trial comparing three contrast doses

OBJECTIVES: To evaluate vascular attenuation (VA) in conventional and low-energy virtual monoenergetic images (LEVMI), volumetric lung iodine density (VID) and quality of CT pulmonary angiography (CTPA) in dual-layer detector spectral CT using three iodinated contrast medium (ICM) administration protocols. MATERIALS AND METHODS: A prospective randomized single-center study including patients with CTPA to rule out pulmonary embolism (PE) was performed. Examinations were randomized to one of three ICM administration protocols: A, 40 mL at 4 mL/s; B, 30 mL at 3 mL/s; and C, 20 mL of ICM diluted with 20 mL of saline at 4 mL/s. Two radiologists evaluated the presence of PE, VA in conventional images and LEVMI, lung VID, perfusion defects detection, and quality of Z-effective maps. Statistical comparisons were performed between protocols. RESULTS: Fifty patients were randomized to each protocol. In conventional images, VA in pulmonary arteries was above 200 HU in more than 90% in protocols A and B, but only in 70% in protocol C. VA increased in LEVMI, with a minimum value of 269 HU. Differences in pulmonary VA with protocol C were statistically significant. At LEVMI, aortic attenuation was above 100 HU in most examinations. Protocol C presented the worst quality of iodine map and the lowest VID; however, it detected perfusion defects in all PE cases. CONCLUSION: The use of LEVMI provides diagnostic VA levels in pulmonary arteries in all the protocols, and a minimum aortic enhancement in most cases. Even the lowest ICM dose maintains diagnostic iodine maps, although with lower quality and VID. KEY POINTS: Question Do low doses of iodinated contrast medium for spectral CT pulmonary angiography achieve diagnostic vascular attenuation, and do they allow detection of perfusion defects in pulmonary embolism? Findings All three protocols achieved diagnostic pulmonary artery attenuation in low-energy virtual monoenergetic images and detected perfusion defects in all pulmonary embolism cases. Clinical relevance Spectral CT pulmonary angiography enables diagnostic pulmonary vascular enhancement and reliable perfusion defect detection with reduced contrast material doses, supporting safer and more efficient pulmonary embolism imaging protocols.