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Objective To evaluate the image quality of Spectral CT associated with ultra-low volume contrast medium for aorta CTA, compared with conventional 120kvp scan with 70ml contrast medium. Methods 62 patients underwent aorta CTA examination on a spectral CT scanner(Discovery CT, GE Healthcare) were divided into 2 groups. 31 patients were scanned using GSI mode with contrast agent volume of 0.4ml/kg and injection rate calculated as volume/( delay time + exposure time) were the study group. After the examination, images using 55keV and 70keV were reconstructed. Those two sets of images are regarded as set 1 and 2. Another 31 patients scanned using 120kvp with contrast agent volume of 70ml and 5ml/s injection rate were retrospectively reviewed as control group. The obtained images were regarded as set 3. CT values and CNR of aorta and its branches were obtained and compared. The overall image quality was evaluated on a five-point scale. Results were statistically analyzed using rank-sum test, t test and Bonferroni test. Results No significant differences existed in image quality of the renal arteries between set 1 and 3(p=0.468). However, higher CNR values were obtained in set 1 than in set 2 and 3(CNR 18.12±5.89vs12.11±4.07vs13.23±1.89 in ascending aorta; 18.34±5.81vs12.19±3.85vs12.39±1.80 in descending aorta; 16.82±4.47vs11.55±3.71vs 12.44±2.17 in celiac trunk; 17.27±4.73vs11.61±3.21vs12.51±1.94 in renal arteries) (p<0.05), while there was no significant difference between set 2 and 3(P>0.05). CT values for aorta and its branches were(358.47±69.56vs213.80±91.03vs374.46±34.23), (361.17±64.09vs216.22±37.65vs353.72±30.68),(336.89±55.70vs205.01±34.45vs354.28±36.96) and (333.57±54.62vs201.22±34.45vs356.99±54.62)HU for the set 1, 2 and 3, respectively. There were significant differences among the three groups (p=0. 00) and between set 1 and 2, set 2 and 3 (p=0.00). There was no significant difference between set 1 and 3(p>0.05). The amount of contrast agent for each patient in the study group was 28.87±4.42ml, while that in the control group was 70ml. There were significant differences of the contrast medium volume among the two groups (F = 537.09, p=0.00). Conclusion Monochromatic images of 55keV in spectral aortic CTA with ultra-low volume contrast medium was feasible and can provide good image quality compared with conventional 120kVp scan.