Comparison of Contrast Agents During CT Angiography

CTA infusion is administered using a 5 ml/sec IV iodinated contrast infusion. 50-70 ml of iodinated contrast is used for the scan depending on the patient's body habitus. The total contrast dose must not exceed 70 ml. An automated bolus tracking feature (SmartPrep, GE Healthcare, Milwaukee, USA) is used to judge contrast bolus arrival and optimize image quality. Patients will be asked to hold their breaths during scanning for up to 10 seconds. A Field of View (FOV) of 25 cm is adjusted to include the heart from below the carina to just below diaphragm. The aorta will be included in the FOV to exclude aortic pathology (ie. dissection, aneurysm, etc.). For patients in sinus rhythm, prospective ECG gating centered at 75% of the R-R interval is used while those in Atrial fibrillation or HR >65 despite oral and IV medications, a retrospective gating is used. The following parameters are used Tube voltage = 100-120kV (based on body habitus), tube current = 400 mA, gantry rotation speed = 0.35 seconds, slice thickness = 0.625 mm, rows = 64, coverage = 128-160 mm.

Estimated radiation dose is = 2-5 mSv dependent on BMI, cardiac height and heart rate. A post acquisition software (Adaptive Statistical Iterative Reconstruction, GE healthcare, Milwaukee, USA) is used to reduce pixel noise standard deviation (noise) by 30 percent and allows for reduced mA in the acquisition while still yielding diagnostic images, thereby reducing total dose required. At the conclusion of each acquisition, technologists collect a survey of patient satisfaction quantifying side effects of different contrasts: flushing, headache, nausea, and pain at injection site as mild, moderate or severe.

Advantage Workstation 4.6 software (GE healthcare, Milwaukee, USA) is used for post acquisition processing. Readers, who are blinded to the type of contrast media used, assess image quality by measuring contrast enhancement in aorta, LV myocardium, left main, proximal Left Anterior Descending artery, proximal and distal Right Coronary arteries. Subjects with coronary artery bypass graft and stents are excluded. Heart rate (HR) variability during the scan is also evaluated. A comparison of the degree of contrast enhancement of the coronary lumen as well as the differences for each of the four contrast agents will be measured and reported, stratified by 100 kVp and 120 kVp acquisition. The image quality of 17 coronary artery segments will be graded by two cardiologists in consensus with the use of a four-point scale (1= excellent, 2=good, 3=fair , 4= poor enhancement) blinded to contrast agent administration.

Statistical Analysis:

All analysis is conducted using SPSS 18.0 for window (SPSS Inc., Chicago, IL, USA). Comparisons between groups are performed using a Student t-test for continuous variables with normal distributions and the Mann-Whitney U test for continuous variables with non-normal distributions. Categorical variables were analyzed by means of χ2 analysis. Correlation between minimum HR and maximum HR was calculated with the Pearson correlation coefficient. The Cochran-Mantel-Haenszel test was used for analyzing the difference in visual quality between two groups.