Computed tomography angiography: the effect of different chaser flow rates, volumes, and fluids on contrast enhancement

OBJECTIVES: The aim of this study was to intraindividually compare the effect of different chaser flow rates, volumes, and fluids on contrast enhancement in multidetector-row computed tomography. MATERIALS AND METHODS: Multidetector-row computed tomography scanning of 5 dogs was performed under standardized conditions using an adapted injection protocol to ensure an identical iodine delivery rate of 1.0 gI/s and a total iodine dose of 300 mg/kg body weight (iopromide 300 and 370). The contrast medium application was followed by a 10-mL saline chaser at different injection rates (0, 2.7, 4, 6, and 8 mL/s) or by different saline chaser volumes (0, 5, 10, and 15 mL) at a flow rate of 4 mL/s. Furthermore, different chaser fluids (NaCl, hydroxyethyl starch 10%, and Dextran 1%) with different viscosities (hydroxyethyl starch 10% and dextran 1%: 3.28 and 5.98 mPa . s at 37 degrees C) were tested (volume: 10 mL; flow rate: 6 mL/s). Each dog was examined with each protocol. The interval between each computed tomography scan session which included 2 measurements was at least 3 days. Dynamic computed tomography scans were acquired at the level of the cephalic vein, cranial vena cava, pulmonary artery, and ascending and descending aorta. Time-enhancement curves were computed, and pulmonary and aortic peak enhancements as well as time-to-peak were analyzed. RESULTS: Increased saline chaser flow rates or increased saline chaser volumes resulted in increased pulmonary and aortic peak contrast enhancement. Peak enhancement was highest and significantly greater compared with no saline chaser for a flow rate of 8 mL/s (pulmonary artery: 816.8 vs. 471.5 HU, P = 0.0079; ascending aorta: 578.7 vs. 384.1 HU, P = 0.0079; descending aorta: 581.4 HU vs. 390.6 HU, P = 0.0159) and a saline volume of 15 mL (pulmonary artery: 670.2 vs. 453.5 HU, P = 0.0079; ascending aorta: 512.1 vs. 370.6 HU, P = 0.0317; descending aorta: 504.0 HU vs. 394.4 HU, P = 0.0159). No significant differences between the peak times for different saline chasers were found. Different chaser fluids did not exhibit significant differences in peak enhancement or peak time. A time-enhancement curve of the cephalic vein showed that the early effects of the saline chaser involved clearing the vein and pushing the contrast medium to the central circulation. CONCLUSIONS: Saline chasing increases pulmonary and aortic peak enhancement with increasing flow rates and volumes of the chaser. The use of more viscous chaser fluids does not improve contrast enhancement. The early effects of the saline chaser involve clearing the vein and pushing the contrast medium to the central circulation