A low-dose and an ultra-low-dose contrast agent protocol for coronary CT angiography in a clinical setting: quantitative and qualitative comparison to a standard dose protocol

Abstract

OBJECTIVES: To evaluate the impact of a low-dose (LD) and an ultra-low-dose (ULD) contrast protocol for coronary computed tomography angiography (CCTA) on qualitative and quantitative image parameters in a clinical setting.
METHODS: We scanned 120 consecutive patients with a 256-slice CT scanner applying a LD (60 patients, 35-55mL) or ULD (60 patients, 25-45mL) contrast protocol adapted to body mass index (BMI). Visually assessed image quality as well as attenuation measured in each coronary segment were retrospectively compared to 20 consecutive patients scanned with a normal-dose (ND, 40-105mL) contrast protocol.
RESULTS: Visually assessed image quality did not differ significantly among protocols. By contrast, attenuation obtained from the ULD protocol (median contrast volume 35ml) differed significantly from the LD (median 45mL) and ND protocol (median 70mL) in coronary segments (316±52HU versus 363±60 HU and 359±52HU, p<0.001). Attenuation did not differ significantly between the LD and ND protocol. The proportion of patients with inadequate coronary vessel attenuation was significantly higher (p<0.001) in the ULD protocol (37%) compared to the ND (5%) and LD (10%) protocol but did not differ significantly between the ND and LD protocol.
CONCLUSION: In a clinical setting, a LD contrast protocol with a median volume of 45mL is feasible for latest-generation 256-slice CCTA as it yields attenuation comparable to a ND protocol. By contrast, the implementation of an ULD protocol remains challenging. Advances in knowledge: Although not perceived by the naked eye, an ultra-low-dose protocol in a clinical setting yields attenuation below a threshold for diagnostic image quality.