Abstract: Objective:To evaluate the pitch of the thoracic and abdominal MSCT CTA image quality,and compare the radiation dose.Materials and Methods:Collection of clinical suspected thoracic and abdominal vascular lesions in 90 patients,according to the different pitch were randomly divided into 3 groups(n=30),group A:a pitch of 1.375:1,55 mm/s bed velocity;group B:a pitch of 0.984:1,39.37 mm/s bed velocity;group C:pitch,0. 516:1 bed velocity 20.62 mm/s,using the same injection rate and dose of contrast contrast tracking trigger scanning.After obtaining data from imaging director and supervisor technician in a AW4.4 workstation for image quality evaluation.Results:Through the pitch after optimization,A,B,C 3 groups average each patient scan time respectively:(12.60±0.54)s,(17.40±0.44)s,(33.10±1.48)s,DLP respectively:(1 462.50±71.56)mGy.cm, (2 010.55±62.14)mGy.cm,(3 821.58±198.50 the difference between mGy.cm),which was statistically significant(<i<P</i<<0.01);3 groups of effective dose(ED)were:24.96 mSv,34.18 mSv,64.97 mSv,A group than in B group for each ED9.22 reduction in patients with mSv,reduced by 26.97%(9.22/34.18),A group than in C group for each patients 40.01 ED by mSv,was significantly reduced by 61.58%(40.01/64.97).3 groups in the ascending aorta,abdominal aorta,renal hilar level of bilateral external iliac artery end average CT values were:353.00 Hu, 350.77 Hu,350.70 Hu,the difference between the 3 groups was not statistically significant(<i<P</i<<0.05), recombinant vascular definition and display of vascular branching number also no difference.Conclusion:The groups A pitch optimization,fast bed velocity scanning parameters can significantly reduce the patient radiation dose,so as to ensure the image quality and meet the requirements of diagnosis.