Halved contrast medium dose in lower limb dual-energy computed tomography angiography—a randomized controlled trial

OBJECTIVES: To compare vascular attenuation (VA) of an experimental half iodine-load dual-layer spectral detector CT (SDCT) lower limb computed tomography angiography (CTA) with control (standard iodine-load conventional 120-kilovolt peak (kVp) CTA). METHODS: Ethical approval and consent were obtained. In this parallel RCT, CTA examinations were randomized into experimental or control. Patients received 0.7 vs 1.4 mL/kg of iohexol 350 mgI/mL in the experimental- vs the control group. Two experimental virtual monoenergetic image (VMI) series at 40 and 50 kiloelectron volts (keV) were reconstructed. Primary outcome: VA. Secondary outcomes: image noise (noise), contrast- and signal-to-noise ratio (CNR and SNR), and subjective examination quality (SEQ). RESULTS: A total of 106 vs 109 were randomized and 103 vs 108 were analyzed in the experimental vs, control groups, respectively. VA was higher on experimental 40 keV VMI than on control (p < 0.0001), but lower on 50 keV VMI (p < 0.022). Noise was higher on experimental 40 keV VMI than on control (p = 0.00022), but lower on 50 keV VMI (p = 0.0033). CNR and SNR were higher than the control on experimental 40 keV VMI (both p < 0.0001) and 50 keV (p = 0.0058 and p = 0.0023, respectively). SEQ was better on both VMIs in the experimental group than in the control (both p < 0.0001). CONCLUSIONS: Half iodine-load SDCT lower limb CTA at 40 keV achieved higher VA than the control. CNR, SNR, noise, and SEQ were higher at 40 keV, while 50 keV showed lower noise. CLINICAL RELEVANCE STATEMENT: Spectral detector CT with low-energy virtual monoenergetic imaging performed halved iodine contrast medium (CM) lower limb CT-angiography with sustained objective and subjective quality. This facilitates CM reduction, improvement of low CM-dosage examinations, and examination of patients with more severe kidney impairment. TRIAL REGISTRATION: Retrospectively registered 5 August 2022 at clinicaltrials.gov NCT05488899. KEY POINTS: • Contrast medium dosage may be halved in lower limb dual-energy CT angiography with virtual monoenergetic images at 40 keV, which may reduce contrast medium consumption in the face of a global shortage. • Experimental half-iodine-load dual-energy CT angiography at 40 keV showed higher vascular attenuation, contrast-to-noise ratio, signal-to-noise ratio, and subjective examination quality than standard iodine-load conventional. • Half-iodine dual-energy CT angiography protocols may allow us to reduce the risk of PC-AKI, examine patients with more severe kidney impairment, and provide higher quality examinations or salvage poor examinations when impaired kidney function limits the CM dose.