Contrast Injection Protocols For Cardiac Computed Tomography Angiography Using A 16-Channel Scanner In Dogs

Kim JS, Bae YH, Lee GE.

in Conference Proceedings. American College of Veterinary Radiology 2013;54.

Introduction/Purpose: The appropriate contrast injection protocol is essential for accurate diagnostic CT angiography. This study investigated the contrast protocols including iodine dosage, dilution ratio, total volume, and scan delay time for the cardiac CT angiography with quantitative and visual evaluation methods, focused on the mean attenuation of the cardiac chambers and main vessels, uniformity of contrast enhancement, and the delineation of intra-cardiac structures with minimal artifacts in dogs.

Methods: This study was carried out using a cross-over design with four adult beagles using 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 (UD), 1:1 (20), 1:2 (3D), and 1:3 (40). Scan delay forCT studies was evaluated using two methods. In “peak arc type” of time to attenuation curve (TAC), CT images were acquired at the peak attenuation value. In a “plateau type” of TAC, CT scanning was performed twice: once at the beginning (beg) and once at the end of the plateau (end), respectively. The mean attenuation and uniformity of attenuation were calculated from left atrium (LA), left ventricle (LV), right atrium (RA), right ventricle (RV), aorta (AO) and pulmonary artery (PA). The delineation of cardiac structure and artifacts were assessed using a 5-point scale.

Results. In most cardiac chambers and large vessels, the mean attenuation of each structure was within 200-300 Hounsfiled units (HU) when CT scanning was performed using 800 mgl/kg 3Dend and 800 mgl/kg 4Dend protocol. Only AO (442.71 ± 55.42 HU) and LV (306.62 ± 34.47 HU) in 800 mgl/kg 3Dend and AO (356.69 ± 82.64 HU) in 800 mgl/kg 4Dend were above the optimal attenuation value. However, the mean attenuation of each cardiac structure except AO was lower than 200 HU in 300 mgl/kg and 400 mgl/kg dosage regardless of dilution ratio. The CT images showed significantly more uniform contrast enhancement especially in RV using 800 mgl/kg 3Dend and 800 mgl/kg 4Dend protocols compared to other dosages and dilutions (p < 0.05). The intra-cardiac structures in LV (3.83 ± 0.62) and RV (3.18 ± 0.29) were most clearly delineated in 800 mgl/kg 4Dend (p < 0.05). Beam hardening artifacts were minimally detected in 800 mgl/kg 4Dend (4.46 ± 0.26). Streaming artifact, in incomplete vascular or chamber filling was minimally detected in 800 mgl/kg 3Dend (4.21 ± 0.33) and 800 mgl/kg 4Dend (4.79 ± 0.40), respectively.

Discussion/Conclusion: Based on the results of our study, we recommend the 800 mgl/kg 3Dend and 800 mgl/kg 4Dend protocols for cardiac CT angiography to achieve adequate and homogeneous contrast enhancement of each cardiac chamber and large vessel with minimal beam hardening and streaming artifacts in normal dogs.