Ultra Low Iodine Loaded Spectral CT Angiography (CTA)

Ultra Low Iodine Loaded Spectral CT Angiography (CTA) of the Aorta and Lower Limb: A Randomized Controlled Trial

The objectives of this study are: Evaluation of ultra-low iodine load CTA protocols of the aorta and lower extremities. To investigate whether dual-layer in combination with with virtual monoenergetic imaging (VMI) allows for reduction of contrast medium (CM) in CTA of the aorta and lower limbs i with sustained objective and subjective image quality parameters.

CT angiography (CTA) of the aorta and the lower limb is one of the most important tools for diagnostic, evaluation of the severity of the peripheral arterial disease, decision making, treatment planning and follow-up; but usually requires the use of iodine contrast medium. Due to the high prevalence of renal impairment (eGFR < 90 ml/min/1.73m) in the elderly hospitalized population (more than 90% among inpatients aged over 60 years) contrast-medium-induced nephropathy is a major concern in this population. The recently introduced spectral CT technique utilizes x-rays covering a spectrum of energy-levels as opposed to conventional CT in which x-rays are set to one specific energy level. This technology offers many possibilities, such as "boosting" the x-ray contrast effect of iodine. This improves the vascular enhancement of the contrast medium using low-energy, virtual monoenergetic imaging (VNI). The objectives of this study are: Evaluation of ultra-low iodine load CTA protocols of the aorta and lower extremities. To investigate whether dual-layer in combination with with virtual monoenergetic imaging (VMI) allows for reduction of contrast medium (CM) in CTA of the aorta and lower limbs i with sustained objective and subjective image quality parameters.

Patients receive half dosage of iodine contrast agent, and Spectral CT acquisition with Virtual Monoenergetic Images at 40 and 50 kiloelectronVolts (keV).

Patients receive standard dosage of iodine contrast agent, and conventional 120 kiloVolts (kV) polychromatic CT images

Patients receive half dosage of iodine contrast agent, and Spectral CT acquisition with Virtual Monoenergetic Images at 40 and 50 keV.

Patients receive standard dosage of iodine contrast agent, and conventional 120 kv Polychromatic CT acquisition.

Attenuation (x-ray density) is measured in Hounsfield units (HU) digitally by placing a "region of interest" (ROI) circle in the Aorta, common iliac-, femoral- and popliteal arteries on the CT images acquired at the time of inclusion.

Examination quality rated by interventional radiologists on a 4-point scale at the anatomic levels: aorta, common iliac, femoral, popliteal- and calf arteries. Subjective examination quality rating scale: (best) - Excellent: The demarcation of the vessel lumen is excellent, more than sufficient for confident diagnosis or exclusion of stenosis or occlusion. - Good: The demarcation of the vessel lumen is sufficient for confident diagnosis or exclusion of stenosis or occlusion. - Adequate: The demarcation of the vessel lumen is adequate for diagnosis or exclusion of stenosis or occlusion, but with limited confidence. (worst) - Non-diagnostic: There is insufficient demarcation of the vessel lumen for diagnosis or exclusion of stenosis or occlusion.

Based on measurements of attenuation in the aorta, common iliac-, femoral- and popliteal arteries. Diagnostic quality defined as arterial attenuation >200 Hounsfield units (HU)

Image noise was defined as the standard deviation of arterial attenuation measurements (see outcome 1) measured in HU digitally by placing a ROI on the CT-images in the aorta, common iliac-, femoral- and popliteal arteries.

Contrast to noise ratio was defined as: (Arterial attenuation - Background attenuation) / Image noise Arterial attenuation: (see outcome 1) measured in HU digitally by placing a ROI on the CT-images in the aorta, common iliac-, femoral- and popliteal arteries. Background attenuation: defined as attenuation in muscle measured in HU digitally by placing an identical size ROI on the CT-images in muscle tissue at the same anatomical levels as the arterial measurements. Image noise: see outcome 4

Signal to noise ratio was defined as: Arterial attenuation / Image noise Arterial attenuation: (see outcome 1) measured in HU digitally by placing a ROI on the CT-images in the aorta, common iliac-, femoral- and popliteal arteries. Image noise: see outcome 4

Inclusion Criteria: Inpatients and outpatients with kidney function (eGFR) allowing for safe administration of standard contrast dose (as calculated with the OmniVis calculator). Patients with clinical suspicion of disease of the aorta and/or arteries in the lower limb. Referral to CTA diagnosis, treatment planning or follow-up. Exclusion Criteria: Iodine contrast medium allergy Age < 18 years Lack of informed consent Critical ischemia of the lower extremities