Purpose: To determine the optimal time window for scanning the liver with computed tomography (CT) during arterial portography (CTAP).
Materials and methods: After vasodilation and contrast medium injection into the superior mesenteric artery (80 mL at 5 mL/sec), 25 repeated scans were obtained at a single level within 83 seconds in 13 patients. Attenuation was measured on every scan, and time-attenuation curves were created. Enhancement characteristics of the portal vein, liver parenchyma, aorta, and tumors were evaluated.
Results: Parenchymal enhancement of more than 60 HU was achieved between 18 seconds +/- 4 (standard deviation) and 67 seconds +/- 15, and high parenchyma-to-tumor contrast of more than 50 HU occurred between 18 seconds +/- 3 and 62 seconds +/- 14.
Conclusion: To scan the liver within such a narrow time window, a spiral CT technique is necessary. When the above injection parameters are used in CTAP, the spiral CT sequence should be started 20 seconds after the beginning of the injection.