Abstract： Objective To evaluate the feasibility of dual energy spectral CT with 270 mg/ml iodixanol in coronary CT angiography (CCTA).Methods A total of 60 patients with suspected coronary heart disease underwent CCTA.They were randomly divided into 3 groups.Prospectively ECG gated CCTA with 120 kVp were performed on the controlgroup (Group A,n=20).In group B (n=20) and group C (n=20),gemstone spectral imaging(GSI) technique were used and monochromatic images from 60 to 80 keV with increment of 5 keV were obtained to divide into 5 subgroups(B1-B5,C1-C5).Group A and group B used the same contrast medium (iodixanol 350 mg/ml) while Group C used low concentration contrast medium (iodixanol 270 mg/ml).One-way ANOVA analysis was used to compare objective evaluation indices (CT values,image noise,signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the left main coronary artery,proximal segment of left anterior descending branch,proximal segment of left circumflex branch and proximal segment of right coronary artery) of group A and B1-B5.Statistical t-test was performed between group A and C2(with optimal keV).Results CNR of the group B1-B5[(21.2± 3.4),(21.5 ±4.0),(21.5 ±4.0),(21.8 ±4.2),(20.7 ± 3.5)]were increased significantly than group A(16.6± 3.8).No significant differences were found among groups B 1-B4 (P＞0.05).Compared withgroup A,group B2 showed higher CT values of the vessels [(481.4±43.2),(466.7±69.3),(434.1±48.8),(436.3±42.5),(427.4±48.6)HU] and decreased image noise[(28.2±7.3)HU versus (31.1±9.9) HU,P＜0.01].The optimal keV was 65 keV.Compared with group A,group C2 showed no significant differences in CT values[(396.3± 76.3),(390.4 ± 74.4),(359.5±83.1),(358.3±67.7),(365.4±68.2)HU)],image noise[(29.1±5.6)HU],SNR(14.6±4.2) and CNR [(18.4±4.8),t=-1.29-1.40,P＞ 0.05].Conclusion Dual-energy spectral CT with monochromatic reconstruction at 65 keV can provide same good image quality as the routine method while reduce iodine concentration to 270 mg/ml.