OBJECTIVE: The objective of the study was to clarify whether a fixed-duration injection protocol is useful in determining the optimal scan delay time without the need for a bolus-tracking technique.
MATERIALS AND METHODS: Three hundred eighteen patients underwent a helical CT examination using a bolus-tracking technique. All the examinations were performed after administering a nonionic contrast medium (300 or 370 mg I/mL; 2 mL/kg of body weight for patients weighing < 75 kg, 150 mL for those weighing > 75 kg). The patients were assigned to one of three groups according to the injection protocol. The injection rate was alternated to 3 or 4 mL/sec in group 1. The injection duration was 38 or 47 sec in groups 2 and 3, respectively. The aortic arrival time and the 100-H threshold time in each patient were measured. The mean values and the variations in the aortic arrival time and 100-H threshold time according to the injection protocols and the contrast media were compared.
RESULTS: The mean variations (� SD) of aortic arrival times and 100-H thresholds in group 2 (aortic arrival time = 16.1 �2.7 sec, 100-H threshold time = 19.6 � 2.9 sec) were smaller than in groups 1 (16.3 � 3.0 sec and 19.9 � 3.7 sec, respectively) and 3 (16.8 � 3.5 sec and 20.4 �4.1 sec, respectively). However, the range of aortic arrival times and 100-H threshold times was more than 10 sec for all groups. The mean aortic arrival time and 100-H threshold time for all patients were 16.5 and 20.0 sec, respectively, and did not vary significantly with the injection protocol and concentration of contrast medium.
CONCLUSION: The individual variations of the aortic arrival and 100-H threshold times can be reduced using a fixed-duration injection technique, but there are still substantial variations. Therefore, a bolus-tracking technique is recommended for optimal timing of arterial phase scanning.