Feasibility of low tube voltage for comprehensive cardiac computed tomography in patients with a normal body mass index: Image quality and radiation dose

The purpose of this study was to compare the image quality and radiation dose between cardiac computed tomography (CCT) protocols using low tube voltage (100 kV) and conventional tube voltage (120 kV) with a wide ECG modulation pulsing window in patients with a normal body-mass-index (BMI). Fifty-two patients with a normal BMI (18-24 kg/m ²) and coronary calcium score <400 Agatston units underwent retrospectively ECG-gated 64-slice CCT with an ECG pulsing window of 40-80% of the R-R interval. Twenty-six patients were assigned to the 100 kV group and the other twenty-six patients were assigned to the 120 kV group randomly. The image quality of the coronary arteries was assessed by a 4-point scale (1=non-diagnostic to 4=excellent). The effective radiation dose, image noise, mean CT-attenuation values, contrast-to-noise (CNR) and signal-to-noise (SNR) ratios were also evaluated. The 100 kV group and 120 kV group showed no significant differences with respect to image quality scores, CNR and SNR. Even with an average of 38.2% dose reduction, the image quality scores were excellent in 89.6% and good in 10.4% of the coronary segments in the 100 kV group. Interobserver agreement in evaluating image quality (κ=0.91) was good. The 100 kV group had a significantly lower effective radiation dose (mean ± SD, 7.6 ± 0.7 vs 12.3 ± 1.5 mSv), higher image noise levels and mean CT-attenuation values than those of the 120 kV group. Although the image noise level was higher than that in the 120 kV group, the 100 kV protocol significantly reduced the radiation dose of CCT in patients with a normal BMI while its image quality scores, CNR, SNR were not significantly affected.