Kim JH, Bae YH, Lee GE.
Introduction/Purpose: In multidetector computed tomography (MOCT) angiography, delay time for cardiac CT scanning is critical for achieving adequate cardiovascular enhancement in the anatomic region of interest (ROI). The 200-300 Hounsfield unit range (HU) in ROI is reported as optimal vascular and ventricular attenuation value. Contrast enhancement of ROI is affected by concentration of iodine contrast medium, volume and flow rate. The goal of this study is to determin the delay time for achieving adequate and consistent cardiovascular enhancement on the basis of the time attenuation curves (TAC) analysis according to various contrast media formulas.
Methods: This study was carried out using a cross-over design with four adult, beagles according to 12 different contrast formulas. Three different dosages of positive contrast medium (iohexol [300 mgl/ml]), were evaluated: 300 mgl/kg, 400 mgl/kg, and 800 mgl/kg. Additionally, 4 concentrations of positive contrast were evaluated using different dilution factors with 0.9% saline: undiluted (UO), 1:1 (20), 1:2 (3D), and 1:3 (40). Dynamic scanning was performed using an ROI in the aorta at the level of the pulmonary trunk and TAC was achieved with 16-channel MOCT scanner.
Results: According to positive contrast formulas, two types of TAC including “peak arc type” or “plateau type” were obtained. The “peak arc type” of TAC was obtained using the UO formula. In diluted contrast formulas, the TAC shape changed from a “peak arc type” to “plateau type” as the total volume of contrast solution increased. A “peak arc type” showed progressively increase of contrast enhancement and reached the peak quickly and then declined rapidly. This TAC was not suitable for homogeneous contrast enhancement because a precipitous change in the attenuation and the short contrast duration « 7 sec) of optimal attenuation, 200-300 HU. A “plateau type” showed the prolonged peak enhancement before decreasing the attenuation, and provided a longer contrast duration with homogeneous attenuation, considering that the 16 channel MOCT requires approximately 15 sec for cardiac scanning, especially using 800 mgl/kg 3D and 800 mgl/kg 40. From the beginning of the plateau in 800 mgl/kg 3D and 800 mgl/kg 40 formulas, the attenuation of TAC remained above the 400 HU. However, the attenuation of TAC was maintained between 200-300 HU for over 16 sec from the end of the plateau. On the basis of TAC analysis, delay time for cardiac CT angiography was determined at the end of plateau using 800 mgl/kg 3D and 800 mgl/kg 40 formulas.
Discussion/Conclusion: The dynamic CT scanning was performed to determine the optimal delay time and appropriate contrast media formulas in dogs. The diluted contrast solution with large volume provided the longer contrast plateau phase with homogeneous attenuation. The delay time is approximately 4-7 sec after injection of 800 mgl/kg 3D and 800 mgl/kg 40 in normal beagle dogs.