Prospective randomized study for an injection protocol for intravenous contrast media in abdominal and pelvic helical CT

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 he lical CT examination procedure of abdomen and pelvis consisted firstly of a native helical examination of the liver, a second one of the liver after i ntravenous injection of 120 ml nonionic contrast medium with a constant sta rt delay of 50 s, and subsequently a third helical CT of the lower abdomen and pelvis. 125 patients were randomized for examination under different pr otocols, varying the injection flow from 2.0-4.0 ml/s and the time delay be tween the second and the third helical examinations from an additional 20-4 0 s. The efficacy of the contrast injection was checked by region of intere st (ROI) measurements of HUs in aorta, inferior vena cava, and in femoral a rteries 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 ca va, 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 t he third helical examination was started immediately after the second one h ad ended. Adding any delay (20 s, 40 s) led to a reduced contrast in the pe lvic vessels, with a significant reduction in aorta and femoral arteries. Conclusion: For routine abdominal and pelvic helical CT, we recommend an in jection of 120 ml contrast medium with a flow rate of 3.0 ml/s. Contrast-en hanced examination of the liver should be started after 50 s, and examinati on of the lower abdomen and pelvis region should be performed without any f urther delay. This gives an appropriate contrast in the major vessels.