Dual-phase helical CT of the liver: Effects of bolus tracking and different volumes of contrast material

PURPOSE: To evaluate the effects of tracking and volume of contrast material on dual-phase helical computed tomography (CT) of the liver. MATERIALS AND METHODS: CT was performed in 120 consecutive patients. Either 100 mi (groups 1 and 2) or 120 mi (groups 3 and 4) of contrast material was injected at a rate of 4 mL/sec. In groups 1 and 3, the scanning delay was fixed, whereas in groups 2 and 4, scanning delays were determined individually by means of a semiautomatic bolus tracking device. The arterial phase began when splenic enhancement was greater than 10 HU and ended when hepatic enhancement was greater than 20 HU, which characterized the start of the portal venous phase. RESULTS: The mean duration of the arterial phase was 11.6 (100 mi) and 12.2 seconds (120 mi). The arterial phase of the liver within the defined limits was sufficiently timed in only 16 (54%) patients in group 1, 25 (83%) in group 2, and 20 (67%) in group 3, whereas it was significantly (P <.05) better in 28 (93%) patients in group 4. A significantly (P <.05) higher mean parenchymal enhancement in the portal venous phase (63.6 HU +/- 8.5) was obtained in group 4. CONCLUSION: Bolus tracking of a volume of 120 mi provided the most accurate results in dual-phase liver CT.