The institutional review board approved this study, and all patients gave written informed consent. One hundred twenty-five patients scheduled to undergo retrospectively elec-trocardiographically gated 16-de-tector row computed tomographic coronary angiography were prospec-tively randomized into the following five groups with respect to the intravenous administration of a 140-mL bolus of contrast material at 4 mL/ sec: group 1 (iohexol [300 mg of iodine per milliliter]), group 2 (io-dixanol [320 mg 1/mL]), group 3 (iohexol [350 mg 1/mL]), group 4 (iomeprol [350 mg l/mL]), and group 5 (iomeprol [400 mg 1/mL]). Attenuation was measured in the descending aorta and coronary arteries. One-way analysis of variance was used to compare groups. Mean attenuation values in the descending aorta were significantly (P < .05) lower in group 1 and higher in group 5 compared with the mean values in the other three groups. The same pattern was observed in the coronary arteries. Contrast materials with higher iodine concentrations yield significantly higher attenuation in the descending aorta and coronary arteries.
Current data suggest that significant coronary artery stenosis can be detected with 16-detector row computed tomographic (CT) angiography (1-5). As compared with those of the previous generation of four-detector row CT scanners, the increased number of detector rows and faster gantry rotation with 16-detec-tor row CT scanners have improved the diagnostic performance of the technique and reduced the time needed to image the entire heart to approximately 20 seconds (3). The type and iodine concentration of the contrast material used have assumed increasing importance in attempts to optimize the diagnostic yield of CT angiography (6) because the attenuation that can be achieved in the vessels greatly affects image quality (7,8). These considerations are even more important for coronary arteries. Their small caliber, tortuous anatomy, and often-extensive vessel wall disease may require better optimization.
Two main modulable factors affect attenuation: (a) techniques that optimize synchronization between the arterial passage of contrast material and CT data acquisition and (b) the injection parameters used for intravenous administration of contrast material (6).
For optimal synchronization, the bolus-tracking technique can be effectively applied (9). In terms of injection parameters, there are several variables that can be manipulated to increase vascular attenuation: the rate of injection, the volume injected, and the iodine concentration of the contrast material (6). Thus, the purpose of our study was to prospec-tively compare the effects on vascular attenuation, at the level of the descending aorta and the coronary arteries, of different concentrations of three contrast materials at CT coronary angiography.
