Milli-ampere modulation in prospectively and retrospectively electrocardiography gated coronary artery angiography

Objective:To evaluate the impact of prospectively ECG-triggered and retrospectively ECG-gated coronary artery CT angiography(CTA) with milliampere(mA) modulation using a 256-slice CT(MSCT) on image quality and radiation dose.Methods:One hundred and sixty patients undergoing 256-slice coronary CTA were divided into three groups:Group A(50 patients),with retrospectively ECG-gated technique,yet with no mA modulation;Group B(50 patients),with retrospectively ECG-gated technique and mA modulation;Group D(60 patients,with prospectively ECG-triggered axial scan.In group C,32 patients with an average heart rate(HR) of ≤70bpm were scanned with a data acquisition window centered at 75% of the R-R cycle and 28 patients with an average heart rate of 70bpm were scanned with the data acquisition window centered at 40%~50% of the R-R cycle.The coronary artery was segmented according to the American heart association(AHA) 15 segment classification,3 grade system was used to evaluate the image quality:excellent(3 scores),medium(2 scores) and is poor(1 score).≥2 grades were regarded to be qualified.Image noise was measured at the center of ascending aorta arising from the left sinus on axial scan,the differences of noise of these 3 groups were compared.The CT dosage index-volume(CTDIvol),dosage length product(DLP),effective dose(ED) of these three groups were recorded,k=0.014.Statistical analyses were performed for the comparison of image quality,noise,CTDIvol,DLP and ED.Results ①As for the image quality,the rate of segment evaluated was 99.3%(608/612 segments),99.1%(609/615 segments) and 98.9%(732/740 segments),respectively,with no significant statistical differences(P0.01).②As for the rate of excellence,there was no significant statistic difference in these 3 groups,when the average heart rate was 70bpm or ≤70bpm.Yet as heart rate ≥70bpm,no statistic difference was existed in the rate of excellence between Group A and Group B,but did existed between Group A and Group B as well as Group A and Group C.③The values of noise measured in these three groups were 32.95±5.49,32.7±5.14 and 33.47±5.54,respectively,with no significant difference(P0.01).④The CTDIvol,and ED values were(62.52±4.67)mGy and(15.3±1.44)mSv,(50.56±9.76)mGy and(13.05±2.34)mSv,(17.47±7.42)mGy and(3.06±1.23)mSv,respectively,with significant differences in the three groups(P0.01).The radiation dose of Group B was 13% lower than that of Group A and the radiation dose of Group C was 80% lower than Group A.Conclusion:Using prospectively ECG-triggered axial scan with 256-slice CT,radiation dose and the impact of undesired heart rate could be significantly reduced.ECG mA-modulation technique could be used to reduce the radiation dose when cardiac function analysis or dynamic observation of cardiac valve disease were needed.