Nodular hepatocellular carcinoma: Variation of tumor conspicuity on single-level dynamic scan and optimization of fixed delay times for two-phase helical CT

Purpose: The purpose of this work was to determine the optimal delay limes in two-phase helical CT for nodular hepatocellular carcinoma (HCC). Method: Twenty-four patients with nodular HCC (size 2.1-6.7 cm, mean 4.2 cm) were divided into three groups to undergo single-level dynamic CT with 150 mi of contrast material (iodine load of 45 g) at a rate of 3 ml/s, CT acquisition started 10, 30, or 60 s after the injection for each group, respectively, and lasted for 110 or 120 s, The optimal 20 s windows that allowed a tumor-to-liver contrast of >10 HU were determined in the pooled tumor-to-liver contrast curve. Results: The determined temporal windows were 36-56 and 130-150 s, respectively. However, each window was not appropriate in seven (33%) and five (36%) patients because of the individual variations of the contrast curve. Conclusion: There is no optimal fixed delay time that is appropriate in all individual patients. The best delay times are 36 and at least 130 s with our injection protocol.