Radiation dose reduction by using 100-kV tube voltage in cardiac 64-slice computed tomography: a comparative study

Objective: To evaluate a 100-kilovoltage (kV) tube voltage protocol regarding radiation dose and image quality, in comparison with the standard 120 kV setting in cardiac computed tomography angiography (CCTA).

Methods: 103 patients undergoing retrospective ECG-gated helical 64-slice CCTA were enrolled (100 kV group: 51 patients; 120 kV group: 52 patients). Inclusion criteria were: (1) BMI <28 kg/m(2); (2) weight <85 kg; (3) coronary calcium score <300 Agatston Units (AU). Quantitative image quality parameters were calculated [image noise, contrast-to-noise ratio (CNR), intracoronary CT-attenuation (HU)]. Each coronary artery segment (AHA/ACC-16-segments-classification) was evaluated for image quality on a 4-point scale.

Results: There was no statistical difference in age, gender, BMI and eff. tube current (mAs), and the use of ECG-tube current modulation (50.9% vs. 50% of patients) between both groups. 84.2% of patients in the 100 kV group had zero calcium score or less than 100 AU, the remaining had between 100 and 300 AU. The effective radiation dose was significantly lower in the 100 kV group with mean 7.1 mSv+/-2.4 (range, 3.4-11.1) compared to the 120 kV group with 13.4 mSv+/-5.2 (range, 6.3-22.7) (p<0.001) (dose reduction, 47%). In the 100 kV group, the use of ECG-dependent tube current modulation reduced the radiation exposure (by 44.8%) to 5.3 mSv+/-1.1 (range, 3.4-8.5 mSv) (p<0.001), the dose without was 9.6 mSv+/-1.1 (range, 6.3-11.1). Image noise in the coronary arteries was not different between both groups with 29.8 and 30.5 SD [HU], respectively. CNR in the 100 kV group was with 20.9+/-6.8 for the coronary arteries and with 19.9+/-5.9 for the aorta similar to the 120 kV group. Intraluminal CT-attenuation (HU) of the coronary arteries were higher in the 100 kV group (p<0.001). Image quality on 100 kV scans was excellent in 86.3%, good in 9.2%, acceptable in 3.1% of coronary segments; 1.4% were non-interpretable (in 1/4 due to increased image noise because of BMI >25 kg/m(2)).

Conclusions: The 100 kV protocol significantly reduces the radiation dose in CCTA in patients with a low BMI <25 kg/m(2) and a low calcium load while maintaining high image quality and the advantages of helical scan algorithm.