Objective:To explore the possible influencing factors for image quality of digital subtraction CT angiography(DSCTA).Methods:Vascular model of the skull base was observed using 16-slice spiral CT(Brightspeed elite).(1)Each parameter was scanned for 10 times at both spiral and non-spiral axial view.(2)Two uniform parameters were compared in the same sequence at different exposure intervals(2.3s

3.5s

4.1s

4.7s

5.9s;4s

5s

6s

7s

8s)and different slices(32

41

48

51

55;60

64

72

77

80)and scanned twice.(3)After injection simulation

the vascular model was scanned for 5 times using the same parameters as above and 80 slices were collected at an exposure interval of 2.4s. Results:The subtraction was 100% successful by non-spiral scanning

while 20% by spiral scanning in 10 times. Within the same sequence

the subtraction was successful only if the tube repetition exposure interval time was integrally divided by 0.6s. The subtraction rate was 85%

in different slices used. The tube exposure interval was 9s. The clear vascular image was obtained after scanning for 5 time. Conclusion Home position of tube is critical to the DSCTA image quality and can be maintained only If the tube repetition exposure interval time integrally divided by the rotation speed. Width of detector has no influence on the DSCTA image quality.