CTA contrast enhancement of the aorta and pulmonary artery: the effect of saline chase injected at two different rates in a canine experimental model.

Objective: To investigate the effect of saline chase injected at 2 different rates on computed tomography (CT) angiography.

Materials And Methods: This study was approved by our institutional animal study committee. Three injection protocols were used; contrast injection (24 mL, 0.8 mL/s) without saline chase (protocol A), contrast injection with saline chase injected at the same rate as the contrast medium (protocol B), and contrast injection with saline chase injected at half the rate (0.4 mL/s) of the contrast medium (protocol C). In the 3 dogs used in our study, each of the protocols was applied twice for every dog resulting in a total of 18 sessions of monitoring scans. CT images were acquired every second at the fixed level of the aorta and pulmonary artery (PA). The duration of plateau, plateau deviation, and peak arterial enhancement were computed and compared using the Kruskall-Wallis and Mann-Whitney U test.

Results: Peak contrast enhancements were significantly more delayed with protocol B than with protocol A in both the PA (B: 48 seconds, A: 30 seconds, P=0.024) and aorta (B: 46 seconds, A: 38 seconds, P=0.024). The duration of enhancement plateau was longer with protocol B than with protocol A in PA (B: 14.8 seconds, A: 9.0 seconds, P=0.002) and in aorta (B: 16.2 seconds, A: 11.6 seconds, P=0.004). Protocol C had the longest duration of plateau in both PA (34.5 seconds, P=0.002) and aorta (33.8 seconds, P=0.004) with uniform plateau enhancement. The peak enhancement values of protocol C, however, were substantially lower than that of protocol A and B in both the PA (A: 262 HU, B: 239 HU, C: 191 HU, P=0.001) and aorta (A: 263 HU, B: 268 HU, C: 210 HU, P=0.001).

Conclusions: Saline chase prolongs the duration of plateau and delays peak enhancement of the pulmonary artery and aorta. Saline chase injected at half the rate of contrast medium injection allowed more uniform and prolonged plateau contrast enhancement than other protocols.