Abstract: Objective:by comparing the image quality,reduce the dosage of contrast agent in pulmonary CTA(CTPA) in clinical application.Materials and methods:using Siemens 64 rows of 128 layer spiral CT,60 cases of clinically suspected pulmonary embolism(PAE) were randomly divided into A,B,C 3 group(n = 20),group A:contrast agent 60 mL + 40 mL saline,group B:contrast agent 30 mL + 40 mL saline,group C:contrast agent 20 mL + 40 mL saline,the other scanning parameters were identical,the contrast agent tracking automatic triggering scanning.Will obtain the original data to the workstation,by 1imaging department deputy chief physician and chief technician,in the axial position measurement of pulmonary artery trunk,left,right pulmonary artery from the descending branch of right pulmonary vein and left,CT value,and the vascular enhancement degree,evaluation of recombinant vascular branches.Results:A,B,C 3 group in the pulmonary trunk,left,right pulmonary artery from the descending branch of the average CT values are:(513.20 Hu,504.34 Hu,509.54 Hu),(498.14 Hu,497.43 Hu,499.63 Hu),(486.31 Hu,489.45 Hu,491.49 Hu),the difference between the 3 groups was not statistically significant(P ＞ 0.05),3 groups of left,right pulmonary vein average CT values are:(235.41 Hu,176.31 Hu,119.91 Hu),(241.01 Hu,169.52 Hu,129.54 Hu),difference has statistics significance(P ＜ 0.05),between groups of pulmonary arteriovenous is statistically significant(P ＜ 0.01);recombinant lung vascular definition and branch vessels showed no significant differences(P ＞ 0.05).Conclusion:a small dose of contrast agent(20 mL/time) in CTPA is feasible,not only reduces the contrast agent(CM) on patients of potential hazards,and save the cost of examination.