Objective To study the effects of two different methods of high-pressure injections on imaging quality of synchronous left axillary artery and vein by using volume CT.Methods Forty seven patients who underwent left axillary vein and artery CTA examination study were analyzed retrospectively according to the contrast agent injection scheme and was divided into two groups A and B.Group A of 25 patients used protocol A,adopted clinical routine delay scanning method,via right elbow vein inject contrast medium.Group B of 22 patients used protocol B,adopted artery delayed imaging combined with vein direct imaging method,via right elbow vein,left radial vein inject contrast agent,respectively.Both values of CT and contrast to noise ratio (CNR) of two groups were compared,objective image quality was compared by two blinded readers.Mann Whiteny U test was used.Results The median of CT values for left axillary artery in group A was 151.9 HU.The median of CNR values for left axillary artery in group A was 7.4.The median of CT values for left axillary vein in group A was 116.0 HU.The median of CNR values for left axillary vein in group A was 3.83.The median of CT values for left axillary artery in group B was 348.8 HU.The median of CNR values for left axillary artery in group B was 25.3.The median of CT values for left axillary vein in group B was 497.0 HU.The median of CNR values for left axillary vein in group B was 35.4.Both values of CT and CNR in two groups showed significant difference (Z=-5.735,-5.799,-5.863 and-5.863,P＜0.01).All of the median scores in group B were greater than in group A(P＜0.01).Conclusion The enhancement effect of protocol B in the left axillary arteriovenous synchronous imaging is significantly higher than those of protocol A,and demonstrates clear image quality and clearer anatomic relationship.