64-slice coronary computed tomography angiography using low tube voltage of 80 kV in subjects with normal body mass indices: comparative study using 120 kV

Background: The radiation dose of coronary computed tomography (CT) angiography (CCTA) is generally higher than that of CT scans of other parts of the body, and there is concern that the high radiation dose may result in increased cancer risk. Although various techniques have recently been introduced to lower the radiation dose of CCTA, there has been no direct comparison between protocols with 80 and 120 kV. Purpose: To assess the image quality and radiation dose of 80-kV electrocardiography (ECG)-gated CCTA in subjects with a normal body mass index (BMI), compared to 120-kV ECG-gated CCTA. Material and Methods: This retrospective study was approved by our local ethics board, and the requirement of written informed consent was waived. We analyzed the CCTA images of 100 subjects with BMIs <25 kg/m(2). Fifty subjects underwent 120-kV CCTA, and the other 50 subjects underwent 80-kV CCTA. Two blinded observers independently evaluated the subjective image quality of the coronary arteries. The objective image quality (signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]) and radiation dose were also measured in each group. Results: Although the objective image quality of the 80-kV protocol images was significantly poorer than that of 120-kV protocol images (mean SNR, 14.9 +/- 4.7 vs. 19.8 +/- 4.4, P < 0.0001; mean CNR, 15.2 +/- 4.8 vs. 21.6 +/- 4.7, P < 0.0001), there was no significant difference in the subjective image quality between the two groups (mean image score, 4.7 +/- 1.1 vs. 4.5 +/- 0.7 for radiologist 1, P = 0.273; 5.0 +/- 1.0 vs. 4.8 +/- 1.0 for radiologist 2, P = 0.197). The radiation dose was reduced by 70% with the 80-kV protocol and by 88% with the 80-kV and ECG-based tube current modulation than with the 120-kV protocol (3.42 +/- 1.16 and 2.9 +/- 0.8 vs. 11.49 +/- 3.62 mSv, P < 0.0001). Conclusion: The low tube voltage CCTA protocol using 80 kV allows significant reduction of the radiation dose without impairing the subjective image quality in subjects with normal BMIs.