Fixed rate vs fixed injection duration in single-pass contrast-enhanced abdominal multi-detector CT: effects on vascular enhancement

Objectives: To evaluate the effects on vascular enhancement of either a fixed rate (FR) or a fixed injection duration (FID) in single-pass (SP) contrast-enhanced abdominal multi-detector CT (CE-MDCT). Methods: Ninety-nine (54 M; 45 F; aged 18-86 years) patients with nontraumatic acute abdomen underwent a SP CE-MDCT after i.v. injection of 1.7 cc/Kg of a nonionic iodinated contrast media (370 mgI/mL) performed with either a FR (2 cc/s; Group A) or a FID (55 s; Group B). In both groups, patients were further stratified according to total body weight (kg) as follows: 40-60 (L); 61-80 (M); 81-100 (H). Signal- (SNR) and contrast-to-noise ratios (CNR) were calculated for the liver and for both abdominal aorta (AA) and main portal vein (MPV). Statistical analysis was performed by Student t- or Chi-square test for continuous and categorical data, respectively, whereas post hoc analysis was performed by the Mann-Whitney test (P < .05). Results: There were no significant differences in demographic and physical characteristics between Group A (n = 50; 53 ± 20 years; BMI = 23.4 ± 4.4) and Group B (n = 50; 51 ± 17 years; BMI 22.7 ± 4.2). Whereas overlapping findings were observed in the M sub-groups (n = 40), SNR and CNR were significantly higher (P < .01) in Group B for both AA and MPV in the high (H) weight sub-groups (n = 20) while not significant differences were observed in the low (L) weight sub-groups (n = 40) despite a significantly lower injection rate (1.6 ± 0.2 cc/s, P < .01) in Group B. Conclusion: A FID results in an overall better vascular enhancement than a FR in SP CE-MDCT. Advances in knowledge: Single-pass is an optimized contrast-enhanced abdominal CT protocol combining the benefits of vascular and visceral enhancement and characterized by a customized scan delay tailored around a monophasic contrast injection. In single-pass protocol, a fixed injection duration (55 s) results in an overall better vascular enhancement than a fixed rate (2 cc/s) and should be therefore regarded as the injection modality of choice.