Biphasic spiral CT of the liver: automatic bolus tracking or time delay?

The aim of this study was to evaluate the value of automatic bolus tracking for biphasic spiral CT of the liver in comparison with time delay examinat ions. Forty patients scheduled for a biphasic spiral CT of the liver random ly were examined either with time delay of 25 s for the arterial phase and 55 s for the portal-venous phase (n = 20), or with an automatic scan start triggered by contrast enhancement in the aorta (n = 20). Examinations were performed with 120 ml of contrast material and a flow rate of 4.0 ml/s. Den sity measurements of the aorta, of the liver parenchyma, and of the spleen were obtained by means of regions of interest (ROI). The end of the arteria l phase was considered when hepatic parenchymal enhancement was greater tha n 20 HU. In all patients of the group with automatic bolus tracking arteria l scanning was completed in the arterial phase, of the liver. In 25% of pat ients with fixed time delay however, an enhancement of liver parenchyma dur ing arterial phase greater than 20 HU was observed. During the portal-venou s phase there was no significant difference in parenchymal enhancement betw een both groups. Automatic bolus tracking allows an individualized timing o f the arterial phase in biphasic spiral CT of the liver. The timing is more accurate than in time delay scanning.