Determining the optimal timing for early arterial phase hepatic CT imaging by measuring abdominal aortic enhancement in variable contrast injection protocols.

Objective: To find the optimal scan timing for early arterial phase hepatic CT with adequate arterial enhancement after the aortic contrast arrival.

Methods: Sixty patients were divided randomly into three groups, each of which received 2.0 mL/kg of the 300 mgI/mL contrast medium with an injection duration of 30 seconds (Group A, mean rate 3.6 mL/sec); of 25 seconds (B, 4.6 mL/sec); of 30 seconds (3.6 mL/sec) followed by a saline chaser (C).

Results: After the contrast arrival, aortic enhancement increased rapidly for 6-15 seconds (mean, 10 seconds) to the initial peak enhancement in all groups, and then, increased moderately to the maximum aortic enhancement over the following 19, 13, and 21 seconds, respectively. The mean maximum aortic enhancement in Group B (392 HU) and C (360 HU) were significantly higher than that in A (326 HU), respectively. The difference between the initial and maximum aortic enhancement was less than 50 HU.

Conclusion: The optimal timing of the early arterial phase for hepatic CT arteriography is 10-15 seconds after the aortic arrival.