Low-dose CT coronary angiography for prospectively gated axial technique:image quality and radiation dose

Objective:To evaluate image quality and radiation dose for coronary artery computed tomographic angiography(CTA) obtained with low tube voltage and short padding time setting for a prospectively gated axial(PGA) CT technique at low heart rate(HR) and heart rate variation(HRv).Methods:Eighty patients enrolled in this study were randomly divided into two groups.Group A consisted of 40 patients with average body mass index(BMI) 20.12 using PGA scan technique(tube voltage was 120kV and tube current was 400mA).Image acquisition was performed at 75% of the R-R interval,and the padding time setting was 100ms.Group B consisted of 40 patients with BMI 20.42 using PGA scan technique(tube voltage was 100kV and tube current was 400mA).Image acquisition was performed at 75% of the RR interval,and the padding time setting was 50ms.The two groups were evaluated for image quality,mean attenuation,noise,signal-to-noise ratio(SNR),contrast-to-noise(CNR) in aortic root and radiation dose.Image quality and radiation dose were analyzed by Mann-Whitney U-test and unpaired t-test.A P value below 0.05 was considered to be statistically significant.Results:The mean effective dose,being statistically significant,for Group A was 3.35mSv versus 1.57mSv for Group B(t=20.084,P0.00001).The mean image quality score was 4.69 for Group A versus 4.37 for Group B(Z=-8.534,P0.00001).The mean attenuation,noise,SNR and CNR were statistically significant for group A versus group B(P0.05).The percentage of assessable coronary artery segments was not statistically significant for group B versus group A(χ2=0.677,P=0.411).Conclusion:Low tube voltage and short padding time setting for PGA CT technique could offer assessable image quality and substantially reduced effective radiation dose at low HR and HRv.