Image quality of low-energy pulmonary CT angiography: comparison with standard CT.

OBJECTIVE: The purpose of this article is to prospectively compare visualization of central and peripheral pulmonary arteries on simultaneously acquired low-energy and standard pulmonary CT angiography. SUBJECTS AND METHODS: Thirty-three consecutive patients (20 women and 13 men; mean age, 55.6 years; range, 21-92 years) with suspected pulmonary embolism (PE) were scanned (140 kVp; 250-300 mA) on a single-source dual-layer dual-energy MDCT scanner. Attenuation and image noise were measured at the main and segmental pulmonary arteries. Signal-to-noise ratios were calculated. Two blinded experienced radiologists assessed segmental and subsegmental artery visibility in consensus, using slab maximum-intensity-projection (MIP) reconstructions. Nonparametric sign test and kappa statistic were used for statistical analysis. RESULTS: PE was detected in three patients (9.1%); two segmental vessel and subsegmental emboli were seen in the low-energy images only. Higher attenuation was noted in low-energy versus standard images for all arteries evaluated, with a mean (± SD) increase of 66.6 ± 4.4 HU (p < 0.0001). Low-energy images improved visualization of segmental and subsegmental arteries from 97.0% to 99.2% and from 88.0% to 93.9%, respectively. A larger number of subsegmental vessels was seen on low-energy MIP reconstructions in 69.7% (95% CI, 36.5-71.89%) of studies compared with 9.1% on the standard images. Visualization of subsegmental vessels was superior in 55.5% of cases using low-energy imaging. The mean image noise increased by 9.7 ± 0.6 HU (p < 0.0001). The mean signal-to-noise ratio showed no significant difference in the low-energy (8.2) versus standard (8.1) CT images (p = 0.7759). CONCLUSION: Improved visualization of central and peripheral arteries can be obtained with low-energy pulmonary CT angiography, without a substantial decrease in image quality.