Hypervascular hepatocellular carcinomas: Bolus tracking with a 40-detector CT scanner to time arterial phase imaging

Purpose: 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. Materials and Methods: 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. Results: 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). Conclusion: Peak TLC during the HAP occurred 18 seconds after triggering.