Introduction Iodine contrast protocols have not been updated parallel to the introduction of 1-rotation scanners that acquire the whole heart without table motion. This reduces significantly the time between bolus tracking and rapid exposure and potentially allows contrast volume savings. A KV-guided stepwise protocol was developed to reduce contrast injection volume to achieve the same aorta attenuation values as conventional protocol (70 mls at 5 mls/s and a delay around 20 s).
Methods Forty-nine outpatients investigated by 320 multidector computed tomography coronary angiography using conventional protocol achieved baseline attenuation more than 400 HU in ascending aorta. Further 320 patients were prospectively scanned with automatic selection of 80 kV, 100 kV or 120 kV based on planning scanogram. Initial contrast volume was based on literature review that suggested 40 mls for standard patient. Contrast reduced in three steps from 70 ml to 35–45 ml to 30–40 ml to 25–40 ml, injected at 4.0 ml/s to 7.0 ml/s.
Results Attenuation values achieved greater than 400 HU in the ascending aorta with 25 ml@4 ml/s at 80 kV and 30 ml@6 ml/s at 100 kV scanning. At 120 kV, attenuation decreased significantly on reducing the volume of contrast from 45 ml to 40 ml injected at 7 ml/s, achieving mean 326 HU in the ascending aorta. Five examinations were suboptimal.
Conclusions Stepwise reduction confirmed low level of contrast volume injection to maintain conventional attenuation levels in the ascending aorta with appropriate flow rates. At 120 kV, the lowest tested volume of 40 mls@7 ml/s was insufficient. Automatic KV selection can determine appropriate contrast volume to be used, similar to weight based algorithms.
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