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 120/80mmHg, HR 60bpm) was used. A fixed CM injection protocol was used for each kVp setting (300mgI/ml [Iopromide], volume=45ml, flow rate=6.0ml/s, iodine delivery rate [IDR]=1.8gI/s, iodine load=13.5gI; at 120, 100, 80 and 70kVp). Then, IDR was decreased by steps of 0.2gI/s for each kVp setting, until diagnostically insufficient attenuation values were reached (<325HU). In order to keep injection time constant (7.5s), total iodine load (TIL) was reduced accordingly. Second, clinical applicability at 120 and 100kVp 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': 1s; 'adaptive sequence' and 'helical': 7s). 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: 335HU±31 (120kVp); 425HU±30 (100kVp); 587HU±29 (80kVp); 666HU±27 (70kVp). Keeping diagnostic enhancement levels (353HU±28) CM could be reduced as follows: 12% for 100kVp; 45% for 80kVp and 56% for 70kVp. Diagnostic enhancement levels could be reproduced with concurrent CM reduction (-12% at 100kV) in the clinical setting (382HU±35). CONCLUSION: CM injection parameters can be substantially reduced at low kVp settings (up to 56% at 70kVp), 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.