Hypervascular Hepatocellular Carcinomas: Bolus Tracking with a 40-Detector CT Scanner to Time Arterial Phase Imaging

Abstract

To evaluate prospectively bolus tracking to time hepatic arterial phase (HAP) imaging of hypervascular hepatocellular carcinomas (HCCs) with a 40-detector computed tomographic (CT) scanner. This study received institutional review board approval; informed consent was obtained. The study included 192 patients (123 men, 69 women; mean age, 67.6 years) with known or suspected HCC who underwent dynamic CT, including HAP scanning; CT depicted 111 hypervascular HCCs in 72 patients. Scanning was performed with a 40-detector CT scanner, and bolus tracking was used to time the start of HAP imaging. Patients were randomly assigned to five protocols; HAP scanning was started at a specified interval after trigger threshold was reached: 9 seconds (protocol A), 12 seconds (protocol B), 15 seconds (protocol C), 18 seconds (protocol D), or 21 seconds (protocol E). Trigger threshold level was set at 100 HU above aortic baseline CT number. Enhancement values in the aorta and the tumor-liver contrast (TLC) were measured. Dunnett multiple comparisons were performed to compare enhancement values among the five protocols. Mean scanning time for the whole liver was 2.1 seconds. Mean enhancement value of the aorta in protocols A, B, C, D, and E were 284.3 HU +/- 54.7, 293.8 HU +/- 51.0, 308.7 HU +/- 55.9, 291.5 HU +/- 42.2, and 235.5 HU +/- 51.2, respectively. Aortic enhancement was significantly lower in protocol E than in protocol A (P < .01); there was no significant difference between protocols A and B, A and C, and A and D. Mean TLCs in protocols A, B, C, D, and E were 23.4 HU +/- 7.6, 35.5 HU +/- 14.0, 36.2 HU +/- 6.8, 47.2 HU +/- 19.2, and 35.1 HU +/- 15.8, respectively. A significant difference was found only between protocols A and D (P < .01). Peak TLC during the HAP occurred 18 seconds after triggering.