Low kilovoltage computed tomography to reduce contrast medium dose in patients at risk of acute kidney injury

Background: Patients with reduced renal function may be at risk of contrast medium-induced acute kidney injury (CI-AKI) following intravenous iodine contrast medium (CM) enhanced computed tomography (CT). Reducing the CM dose may reduce this risk. Decreasing the X-ray tube potential (kilovoltage, kV) from commonly used 120 to 80 kV results in higher CM attenuation due to the photoelectric properties of iodine, which may permit reduction of the iodine dose while keeping the attenuation unchanged. Lower tube potential, however, increases image noise which may be controlled by increasing the X-ray tube loading (milliampere seconds, mAs) to keep image quality, e.g. contrast-to-noise ratio (CNR) unchanged. Complete compensation of tube loading increases the radiation dose to the patient, but the introduction of noise reducing iterative reconstruction algorithms may prevent this. Aim: To investigate if low-kV CT with reduced CM doses is a feasible alternative in examinations of the thorax and abdomen in patients considered at risk of CI-AKI. Material and methods: In three cross-sectional studies 80-kV CT protocols with 40-50% reduction of CM dose and increased tube loading to control image noise was compared with standard 120-kV protocols, in two studies to diagnose pulmonary embolism and in one hepatic study. Based on a phantom study and a clinical hepatic CT study, iterative reconstruction algorithms were used to control image noise with no increase in tube loading. Image quality was evaluated objectively and subjectively. Results: Using 80-kV CT protocols with reduced CM doses (40-50%) and mAs compensation seems to provide satisfactory diagnostic quality in pulmonary CT angiography and hepatic CT for patients with GFR <45-50 mL/min and a body mass index <30 kg/m2. However, the use of iterative reconstruction algorithms to control image noise without increased mAs resulted in inferior subjective image quality. Conclusion: Using low-kV CT protocols with reduced CM dose could benefit patients at risk of CI-AKI. The usefulness of iterative reconstruction algorithms to control image noise and not increase radiation dose remains unclear.