The effect of chest circumference index adjusting tube voltages technique on image quality and radiation dose at coronary CT angiography

Objective: To explore the effect of chest circumference index adjusting tube voltage technique on image quality and radiation dose at coronary CTA. Methods: One hundred and twenty consecutive patients [body mass index(BMI) < 25 kg/m²] with suspected coronary heart disease (CHD) undergoing coronary CT angiography were prospectively selected and divided into 2 groups at random: conventional group and low dose group. Low dose group was divided into the following three subgroups according to different chest circumferences: A group(< 80 cm, n = 16), B group(80 to 90 cm, n = 44) and C group (> 90 cm, n = 20). All patients were examined by coronary CTA. The patients in conventional group were performed using retrospective ECG-gating technology and reconstructed by filtered back projection algorithm. The tube voltage/tube current was 120 kV/1000 mAs. Prospective ECG-gating technology and iterative algorithm reconstruction were used in low dose group. The tube voltages/currents were 80 kV/150 mAs, 100 kV/150 mAs, 120 kV/150 mAs in A, B, C group, respectively. Image quality was assessed by subjective evaluation (image quality score) and objective evaluation (signal-to-noise ratio).The effective radiation dose was calculated. Analyses of the differences between groups were compared with image quality, radiation dose by single factor variance and Wilcoxon signed ranks test. Results: The image quality scores and signal-to-noise ratio of aorta were respectively (3.47 ± 0.38), (3.48 ± 0.27), (3.45 ± 0.32), (3.46 ± 0.29) and (15.5 ± 3.6), (15.8 ± 3.6), (15.8 ± 4.1), (16.2 ± 3.9) in conventional, A, B and C groups, there was no statistical difference between the four groups (P = 0.24, 0.43). The effective radiation dose of four groups were respectively (17.15 ± 3.25), (0.88 ± 0.02), (1.38 ± 0.05), (2.32 ± 0.04) mSv, the difference was statistically significant (P = 0.02). The effective radiation dose of A, B, C group was significantly lower than that in the conventional group. Conclusion: Chest circumference index adjusting tube voltages technology at coronary CT angiography can effectively reduce the effective radiation without compromise of image quality. (authors)