Helical CT of the liver : evaluation of injection flow rate, mode, and scan delay with a reduced-volume contrast medium bolus

The impact of injection flow rates, mono- or biphasic injection mode, and scan delay on liver and portal vein enhancement with helical CT was evaluated. The liver of 75 consecutive patients was examined with helical CT before and after injection of 100 ml iopromide (30 g of iodine). Patients were randomly assigned to three protocols: (1) injection flow: 2 ml/s; (2) injection flow; 4 ml/s (60 ml) + 2 ml/s (40 ml); and (3) injection flow: 4 ml/s. Scanning started 40 s after the beginning of contrast material injection. A second scan was performed 70 s after contrast agent injection in Protocol 1. Mean parenchymal contrast enhancement was highest with Protocol 3 (48.5 HU) followed by Protocols 2 (38.9 HU) and 1 (early: 21 HU; late: 30.7 HU), with all differences being significant (p < 0.01). Enhancement of the portal vein was significantly higher with Protocols 3 and 2 (121 and 118 HU) than with Protocol 1 (early: 64 HU; late: 75 HU). Good enhancement of the liver parenchyma and the portal vessels can be obtained with 30 g of iodine if a monophasic injection with a flow rate of 4 ml/s is used.