Helical CT of the liver with computer-assisted bolus-tracking technology: Scan delay of arterial phase scanning and effect of flow rates

Purpose: The purpose of this work was to assess the scan delay and the effect of flow rates on arterial phase scanning of hepatic CT. Method: One hundred twenty patients suspected of having hepatocellular carcinoma were examined by three-phase helical CT using computer-assisted bolus-tracking technology. We set the region of interest (ROI) in the abdominal aorta at the level of the celiac artery as a baseline. The triggering threshold was set at 100 HU. A volume of 100 ml of iomeprol (350 mg of I/ml) was administered at 2, 2.5, or 3 ml/s i.v. Results: In all cases, helical CT scanning began after reaching the ROI threshold. Then, portal venous phase scanning was initiated 50 s after arterial phase initiation. The mean delay time from the initiation of contrast agent administration to the beginning of arterial phase scanning was 29.2 +/- 3.8 a (mean +/- SD, range 22-39 s). A faster injection rate significantly shortened the scan delay (p < 0.01). In portal venous phase scanning, calculated areas under the hepatic enhancement curves were almost equal among different injection rates. Conclusion: The computer-assisted bolus-tracking technology is a useful method for determining an individual scan delay of arterial phase CT.