Optimizing scan delays of fixed duration contrast injection in contrast-enhanced biphasic multidetector-row CT for the liver and the detection of hypervascular hepatocellular carcinoma.

Objective: To determine the optimal scan delay required for fixed duration contrast injection in contrast-enhanced biphasic multidetector-row CT for the liver and the detection of hypervascular hepatocellular carcinoma (HCC).
Methods: CT images (2.5-mm collimation, 5-mm thickness with no intersectional gap) were obtained after an intravenous bolus injection of 2 mL/kg of nonionic iodine contrast material (300 mg I/mL) for a fixed 30-second injection in 206 patients, who were prospectively randomized into four groups, for which scans were initiated at -5, 15, and 35 seconds; at 0, 20, and 40 seconds; at 5, 25, and 45 seconds; or at 10, 30, and 50 seconds for the first (acquisition time: 4.3 seconds), second (4.3 seconds), and third (9.1 seconds) phases, respectively, after the completion of contrast injection. Mean CT values (HU) of the abdominal aorta, spleen, main portal veins, liver parenchyma, and hepatic veins were measured. Increases in CT values between pre- and post-contrast CTs (DeltaHU) for the organs, and spleen-to-liver and HCC-to-liver contrast differences (deltaHU) were assessed.
Results: Abdominal aorta reached 273-301 DeltaHU at -5 to 10 seconds with a peak (301 DeltaHU) at 5 seconds. Spleen peaked (115 DeltaHU) at 10 seconds. Liver parenchyma were enhanced weakly (11-34 DeltaHU) at -5 to 10 seconds, exceeded 50 DeltaHU at 20 seconds, peaked (61 DeltaHU) at 30 seconds, and then plateaued (54-58 DeltaHU) at 35-50 seconds. Hepatic veins were enhanced weakly (14-37 DeltaHU) at -5 to 10 seconds, and reached 67 DeltaHU at 15 seconds. Spleen-to-liver (65-69 deltaHU) and HCC-to-liver (31-34 deltaHU) contrast differences were highest at 5-10 seconds. Qualitative results corresponded well with quantitative results.
Conclusions: For the detection of hypervascular HCCs, the optimal scan delay after a 30-second contrast injection of the hepatic arterial phase, was found to range from 5 to 10 seconds, and that of the portal venous phase was 35 seconds or somewhat longer.