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Coronary Angiography by 64-Detector Row Computed Tomography Using Low Dose of Contrast Material with Saline Chaser: Influence of Total Injection Volume on Vessel Attenuation

Objective: To assess the influence of total injection volume on thoracic great vessels and coronary arteries enhancement in 64-detecter row computed tomography (CT) coronary angiography using low dose of contrast material. Methods: Sixty patients underwent cardiac CT (64 × 0.5 mm, 0.4 rot/s) using 40 mL of contrast material (350 mg of Iodine per milliliter) in 30 patients and 50 mL in 30 patients. Computed tomography densities (Hounsfield units) in ascending aorta, descending aorta, and main pulmonary artery were measured at every second with the time of CT data acquisition recorded in each reconstructed image. Computed tomography densities of proximal and distal coronary arteries were also measured. Differences in CT densities between 40 and 50 mL contrast material were assessed with the Student t test. In addition, the relation between the injection volume (mL) of contrast material per kilogram body weight and contrast enhancement in coronary arteries was studied. Results: The average attenuations in the ascending and descending aorta and coronary arteries were significantly lower in 40-mL group than in 50-mL group (<0.05). In addition, the average attenuations in the pulmonary artery were significantly lower in 40-mL group than 50-mL group (<0.01). Every patient with the total injection volume of more than 0.9 mL/kg body weight showed a contrast enhancement more than 250 Hounsfield units. Conclusions: The reduction of total injection volume lowered the enhancement of thoracic great vessels and coronary arteries in 64-detector row cardiac CT. The injection volume of at least 0.9 mL/kg body weight was necessary for a steady contrast enhancement in coronary arteries.