Abstract: Objective To evaluate the correlation between image quality and thoracic diameters, anteroposterior diameter (AP) and right-left diameter(RL) for the optimization of reducing radiation dose in coronary artery imaging with Dual-source CT. Methods 118 patients underwent CT coronary artery imaging(CTCA)were divided into two groups (A and B) according to body mass index (BMI). There were 58 patients in group A with BMI values ≥ 25 kg/m² and <30 kg/m²; and 60 patients in group B with BMI values <25 kg/m². Scan parameters:collimation 64×0.6 mm, reconstruction slice thickness 0.75 mm, reconstructin interval 0.7 mm, FOV 150-180 mm, the pitch adjusted according to heart rate automatically. CT imagings were obtained with tube voltage 100 kV, tube current 330 mAs (group A) and 100 kV, tube current 220 mAs (group B). The contrast-noise ratio (CNR), signal to noise ratio (SNR),as well as blind correlation test score values were calculated to establish the relationship among BMI, AP, RL and CNR, SNR; Results RL of five levels in groups of A, B were correlated to CNRa (P<0.05). In group A and B (except iii, iv level of Group A), AP were associated with CNRa (P<0.05). In addition to ii, iv level of group A, v level of group B, BMI were associated with CNRa (P<0.05). The correlation coefficient of CNRa and RL of group A except ii level was greater than that of CNRa and AP. The correlation coefficient of CNRa, SNRa and RL of group B was greater than that of CNRa, SNRa and AP. Except iii level, the correlation coefficient of CNRa, SNRa and AP of group A was greater than that of CNRa, SNRa and BMI. Except ii level, the correlation coefficient of CNRa and AP of group B was greater than that of CNRa and Conclusion Thoracic diameter of RL can be used as a guider to select the appropriate scan protocol in the coronary imaging acqusition with dual-source CT.