PURPOSE: To evaluate the influence of different injection rates and different threshold levels on hepatic enhancement using the bolus tracking technique. MATERIALS AND METHODS: One hundred patients were included in this randomized and prospective study performed on a helical CT. Patients were assigned to one control and four study groups. Each group received 150 ml nonionic contrast medium. In the control group, used delay time and injection rate were 60 sec and 3 ml/sec, respectively. In the study groups, two different injection rates, 3 ml/sec (groups 1 and 2) and 5 mL/sec, respectively. In study groups, two different preselected thresholds, 40 HU (groups 1 and 3) and 50 HU (groups 2 and 4) were used. In these groups, delay times were determined individually by means of the bolus tracking technique. Peak enhancement time (PET), peak enhancement value (PEV), and mean hepatic enhancement (MHE) on CT scans was calculated for each group. RESULTS: PET was found to be significantly earlier in the study groups in which the injection rates were 5 mL/sec, compared to the other groups (p < 0.001). MHE was significantly higher in all study groups compared to the control group (p < 0.001). PEV was higher in study groups that the preselected threshold was 50 HU compared to only the control group (p < 0.01). CONCLUSION: Use of a bolus tracking program helps to achieve a greater level of hepatic enhancement. Increasing the injection rate shortens the time to peak hepatic enhancement. The threshold level of 50 HU achieves a great level of hepatic enhancement independent of injection rates in the bolus tracking technique. If the bolus tracking technique is not available, using an injection rate of 3 ml/sec and 70 sec delay time seems to be appropriate.