Reduced Iodine Load at CT Pulmonary Angiography with Dual-Energy Monochromatic Imaging: Comparison with Standard CT Pulmonary Angiography—A Prospective Randomized Trial

To compare quantitative and subjective image quality and radiation dose between standard computed tomographic (CT) pulmonary angiography (CTPA) and CTPA with a dual-energy technique with reduced iodine load. This prospective study was approved by the institutional review board and each participant provided informed consent. Ninety-four patients (59% male; mean age ± standard deviation, 62 years ± 15) were randomized to one of two protocols: standard CTPA (100-120 kVp) with standard contrast medium injection (n = 46) and dual-energy CTPA (image reconstruction at 50 keV) with the same injection volume as in the standard protocol but composed of contrast medium and saline in a 1:1 fashion, resulting in 50% reduction in iodine load (n = 48). Signal intensity and noise in three central and two segmental pulmonary arteries were measured; signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. A five-point scale was used to subjectively evaluate vascular enhancement and image noise. The proportion of diagnostic (score, ≥ 3) studies and the interreader agreement regarding the dichotomized diagnostic versus nondiagnostic scale were compared between the two groups. Compared with standard CTPA, dual-energy CTPA demonstrated higher signal intensity in all pulmonary arteries (all P < .01), inferior noise only in segmental arteries (P < .05), higher SNR and CNR (both P < .05), and compatible effective dose (P > .05). The five-point score was higher in the standard CTPA protocol (P < .05). The interreader agreement regarding the dichotomized diagnostic versus nondiagnostic scale was similar (P > .05) between the two groups. Dual-energy CTPA with image reconstruction at 50 keV allows a significant reduction in iodine load while improving intravascular signal intensity, maintaining SNR and with comparable radiation dose.