Factors influencing vascular and hepatic enhancement at CT: Experimental study on injection protocol using a canine model

Purpose: The purpose of this work was to evaluate the effects of contrast m edium injection parameters on aortic, portal vein, and hepatic enhancement at spiral CT and to assess optimal injection protocol for hepatic CT. Method: Ten 15 kg dogs underwent single level dynamic CT through the hepati c hilum at 5 s intervals just after the injection of contrast medium for 3 min. With use of different volumes (1, 2, and 3 ml/kg), injection rates (0. 5, 1, and 2 ml/s), and concentrations (150, 200, and 300 mg/ml), a total of 270 spiral CT scans were performed. In each scan. time-attenuation curves of aorta, portal vein, and liver were obtained. The degree of maximum contr ast enhancement (I-max), time to maximum enhancement (T-max), and time to e quilibrium phase (T-eq) for to each injection protocol were analyzed. Results: Alterations in contrast material volume, injection rate, and conce ntration had significant impact on contrast enhancement of the liver. With increasing volume of contrast medium, I-max, T-max, and T-eq of aorta, port al vein, and liver increased (p < 0.005). With increasing rate of injection , on the other hand, I-max of aorta and liver increased (p < 0.05), but T-m ax and T-eq decreased (p < 0.005). Change of concentration of contrast medi um had a significant effect on I-max of vessels (p < 0.05). Conclusion: Maximum contrast enhancement of liver and vessels was influence d mainly by injection volume of contrast medium and the time to peak enhanc ement by injection rate of contrast medium. Under given amounts of contrast medium, therefore, the strategy of increasing volume by dilution and faste r injection might give better I-max values without penalty for the duration of an optimal temporal window (T-max and T-eq).