An Optimized Test Bolus Contrast Injection Protocol for Consistent Coronary Artery Luminal Enhancement for Coronary CT Angiography

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Consistent levels of coronary artery enhancement are essential for quantitative analysis of coronary artery plaque. We studied three contrast injection protocols for coronary CT angiography (CCTA) and compared mean attenuation level and consistency of vascular contrast enhancement. We hypothesized that test bolus adjusted protocols will have a superior consistency of coronary attenuation compared to a weight-based protocol. We prospectively evaluated a standard test bolus injection protocol (protocol 1, 32 subjects) and an optimized test bolus injection protocol (protocol 2, 59 subjects) in comparison to a body weight-based injection protocol (60 subjects). The test bolus was diluted contrast (20%-30% iopamidol 370 mixed with normal saline); peak aortic attenuation was measured and used to calculate a specific water/contrast mixture for the CCTA. The mean attenuation of the coronary lumen was measured on CCTA. Metrics of optimum arterial enhancement included the percentage of patients within a predetermined range for coronary attenuation (325-500 HU) and optimal timing with maximal ascending aortic attenuation. In addition, interpatient variation in coronary enhancement was quantified as percentage standard deviation of the attenuation. The mean attenuation of the coronary arteries was similar in all protocols (362, 364, and 375 HU for the weight-based, test bolus 1 and 2 protocols, respectively). The percentage standard deviations of the weight-based, test bolus 1 and 2 protocols for coronary attenuation were 25.3%, 27.1%, and 10.5%, respectively (p < 0.0001). Test optimized bolus protocol 2 yielded the highest percentage of scans within the preferred coronary attenuation range (88%, p = 0.002). In test bolus protocol 2, the contrast timing was optimal in 73% of cases compared to only 22% of cases in the body mass guided injection protocol (protocol 1, p < 0.0001). An optimized test bolus guided injection protocol resulted in a marked reduction in variation in coronary enhancement for CCTA compared to a body weight-based injection protocol.