Abstract
Objective: To develop an injection protocol for intravenous administration of contrast media in abdominal and pelvic helical CT which provides optimal contrast enhancement of arterial and venous vessels.
Material and Methods: for the study on a Somatom Plus 4 unit, a standard helical CT examination procedure of abdomen and pelvis consisted firstly of a native helical examination of the liver, a second one of the liver after intravenous injection of 120 ml nonionic contrast medium with a constant start delay of 50 s, and subsequently a third helical CT of the lower abdomen and pelvis. 125 patients were randomized for examination under different protocols, varying the injection flow from 2.0–4.0 ml/s and the time delay between the second and the third helical examinations from an additional 20–40 s. the efficacy of the contrast injection was checked by region of interest (ROI) measurements of HUs in aorta, inferior vena cava, and in femoral arteries and veins. the results were compared by t-test statistics.
Results: A slow flow rate of 2.0 ml/s led to a higher contrast enhancement in the aorta than a flow rate of 3.0 and 4.0 ml/s. the difference between 2.0 ml/s and 4.0 ml/s was statistically significant. In the inferior vena cava, a flow of 3.0 ml/s caused a better contrast than a flow of 2.0 ml/s or 4.0 ml/s but the measurements did not reach statistical significance. the measurements in the femoral arteries and veins did not show any significant differences. Maximal enhancement in the pelvic vessels was achieved when the third helical examination was started immediately after the second one had ended. Adding any delay (20 s, 40 s) led to a reduced contrast in the pelvic vessels, with a significant reduction in aorta and femoral arteries.
Conclusion: for routine abdominal and pelvic helical CT, we recommend an injection of 120 ml contrast medium with a flow rate of 3.0 ml/s. Contrast-enhanced examination of the liver should be started after 50 s, and examination of the lower abdomen and pelvis region should be performed without any further delay. This gives an appropriate contrast in the major vessels.