Optimizing contrast media application in coronary CT angiography at lower tube voltage: Evaluation in a circulation phantom and sixty patients

Purpose: The purpose was to investigate optimal contrast media (CM) injection parameters for lower kVp settings, whilst maintaining diagnostic attenuation levels. Methods and materials: First, a circulation phantom with physiological parameters (BP 120/80 mmHg, HR 60 bpm) was used. A fixed CM injection protocol was used for each kVp setting (300 mgI/m1 [Iopromide], volume =45 ml, flow rate = 6.0 ml/s, iodine delivery rate [IDR] = 1.8 gI/s, iodine load = 13.5 gI; at 120, 100, 80 and 70 kVp). Then, IDR was decreased by steps of 0.2 gI/s for each kVp setting, until diagnostically insufficient attenuation values were reached (<325 HU). In order to keep injection time constant (7.5 s), total iodine load (TIL) was reduced accordingly. Second, clinical applicability at 120 and 100 kVp was evaluated in patients (n = 60) referred for coronary CT angiography. A standard and reduced (12% less) CM protocol was used based on weight classes and scan duration (`high-pitch': 1 s; 'adaptive sequence' and 'helical': 7 s). Attenuation levels of the coronary arteries were measured and compared between protocols. Results: Using a fixed CM injection at each kVp level resulted in the following HU values: 335 HU +/- 31 (120 kVp); 425 HU +/- 30 (100 kVp); 587 HU +/- 29 (80 kVp); 666 HU +/- 27 (70 kVp). Keeping diagnostic enhancement levels (353 HU +/- 28) CM could be reduced as follows: 12% for 100 kVp; 45% for 80 kVp and 56% for 70 kVp. Diagnostic enhancement levels could be reproduced with concurrent CM reduction (-12% at 100 kV) in the clinical setting (382 HU +/- 35). Conclusion: CM injection parameters can be substantially reduced at low kVp settings (up to 56% at 70 kVp), whilst maintaining diagnostic attenuation levels. This may play an important role in CT imaging of the coronary arteries as well as cerebral and peripheral circulations in the future. (C) 2016 Published by Elsevier Ireland Ltd.