Contrast material concentration (CMC), rate, volume and total iodine load are 4 variables affecting vascular and visceral enhancement in multiphase abdominal CT. Previous studies have documented increased vascular enhancement with higher concentration, rate of injection and iodine load. In this study, abdominal visceral vascular enhancement during late arterial circulatory phase was compared using identical iodine loads injected at different CMC.

Patients undergoing pre or post intervention or surveillance imaging for vascular hepatic neoplasm were prospectively enrolled and randomized into two injection groups, each group receiving the same total iodine load (42gm) at the same injection rate (5ml/sec) but varying in iodine concentration. 60 patients (mean age 52, 33 male, 27 female, mean weight 175 lbs) received 150ml 300mg iodine/ml (IsoVue 300) – injection interval 30 seconds and 60 patients (mean age 53, 40 male, 20 female, mean weight 188 lbs) received 120 ml 370 mg iodine/ml (IsoVue 370) – injection interval 22 seconds. Late arterial/portal vein inflow phase began 15 seconds after aortic peak on a preliminary mini bolus.

All studies were performed with an identical volume flow rate injector (EZM Empower)on an 8 or 16-channel MDCT (General Electric Ultra (8), LightSpeed (16).

Attenuation was measured in the common hepatic, splenic, right and left renal and superior mesenteric arteries and the portal vein.

Mean attenuation value of each target vessel for 300/370 mg iodine/ml injection concentration and 95% confidence intervals for differences were as follows: hepatic artery (273/285 HU,
-41-16), splenic (276/285, -36-18), right renal (275/273, -26-30), left renal (267/267, -28-27), superior mesenteric (289/299, -40-20). There were no statistically significant differences. Mean portal vein attenuation was 175/180.

In the late arterial phase and at equal iodine load, 300 mg iodine/ml concentration contrast produced equivalent abdominal visceral vascular enhancement to 370 mg iodine/ml. Higher CMC is preferred for early arterial phase CT angiography: with equivalent iodine load the effect is not replicated in the late arterial phase.

W.D.F.: W Dennis Foley received an investigator grant from Bracco Diagnostics to conduct this study.