Purpose: We compared the fixed injection rate protocol (P2) with the fixed injection duration protocol (P1) for coronary CT angiography using the test bolus technique.
Materials and methods: We randomly assigned 100 patients to one of two protocols. In P1, they received 0.7 mL/kg Iohexol-350 in an injection duration of 9 s, and we selected a delay of 3 s after peak enhancement of test bolus scan. In P2, they received 0.7 mL/kg Iohexol-350 at an injection rate of 5 mL/s, and we selected a delay after peak enhancement of test bolus scan using the following formula: TID/2-2 s, where TID is the injection duration of full bolus. We compared attenuation values in the ascending aorta and coronary arteries and patient-to-patient enhancement variability at each segment.
Results: At all segments, CT attenuations of P2 were significantly greater than those of P1 (ascending aorta 400 ± 64 vs. 368 ± 60, P = 0.01; left main trunk 399 ± 67 vs. 369 ± 55, P = 0.02; proximal-RCA 393 ± 66 vs. 363 ± 56, P = 0.01). There was no significant difference in patient-to-patient enhancement variability at all segments between the two groups (P > 0.05).
Conclusion: P2 yielded superior vessel enhancement and comparable patient-to-patient enhancement variability compared with P1 in thin patients.