Hepatic CT enhancement: effect of the rate and volume of contrast medium injection in an animal model

Background: To evaluate the relative effect of rate of injection and volume of contrast medium on aortic, portal, and hepatic enhancement during compu ted tomography (CT). Methods: Thirty-eight nonincremental CT examinations were performed in thre e mini-pigs by using a combination of three different volumes (1.5, 2, and 3 mL/kg) and five different rates (1.5, 3, 4.5, 6, and 7.5 mL/s) of contras t material injection. Time-density enhancement curves of the aorta, portal vein, and liver were plotted over time for each rate of injection, each vol ume of contrast, and each volume-rate combination. In addition, aortic, por tal, and liver peak enhancements, time-to-peak enhancements, optimal scanni ng intervals, and contrast enhancement indices were calculated for each vol ume-rate combination. Results: Higher rates of injection increased peak aortic enhancement but ha d no effect on peak portal or hepatic enhancement. This result may be expla ined by the dilution of the bolus of contrast medium in the splanchnic circ ulation. When the results of a 6-mL/s injection of 1.5 mL/kg of contrast ma terial were compared with a 3-mL/s injection of 2 mL/kg, maximum aortic enh ancement increased by 32%, whereas maximum liver enhancement decreased by 3 5%. Conclusion: An increase in the rate of contrast injection results in an inc rease of peak aortic enhancement even when the total iodine load is decreas ed. However, an increase of the rate of contrast injection does not increas e maximum liver enhancement, which is related to the total iodine dose inje cted. Therefore, one cannot compensate a decrease in the iodine load by an increase in injection rate in contrast-enhanced CT of the liver.