CT DETECTION OF LAYERING OF IV CONTRAST MATERIAL IN THE ABDOMINAL-AORTA

OBJECTIVE. We sought to determine whether IV contrast material would l ayer dependently within the abdominal aorta if administered from a loc ation and at a rate routinely used for CT angiography. SUBJECTS AND ME THODS. In 22 patients, three equal-sized regions of interest (ROIs) we re symmetrically spaced across the abdominal aortic lumen at the level of the celiac axis. These positions corresponded to a dependent, a ce ntral, and a nondependent position. Time-enhancement curves were gener ated for each ROI after IV injection of 10 mi of nonionic contrast mat erial, which was administered at a rate of 3.5 ml/sec, through an ante cubital vein. The magnitude of and the time to peak enhancement for ea ch ROI were determined. The 22 peak enhancement values obtained for ea ch of the three ROIs were compared using the Newman-Keuls test. RESULT S. A statistically significant increase in peak enhancement was identi fied when traversing the abdominal aortic lumen from the nondependent to the central ROI (p < .05) and from the central to the dependent ROI (p < .01). Levels of mean peak enhancement were 48.3 +/- 19.0, 38.9 /- 18.2, and 33.0 +/- 19.7 for the dependent, central, and nondependen t ROIs, re respectively. The amount of time needed to reach peak enhan cement of each of the three ROIs in an individual patient was similar. CONCLUSION. A small dose of contrast material administered IV through an antecubital vein will layer dependently in the abdominal aorta-thu s creating a gradient in enhancement-despite mixing in the heart. If l ayering of contrast material is subsequently detected during routine a bdominal CT angiography, then patient positioning may need to be adjus ted to maximize enhancement of targeted vessels.