Abstract: Objective: To compare the image quality of aorta angiography detected by 64-slice spiral CT and 16-slice spiral CT, and to study the effects of different dose of contrast material with the same concentration and the same injection rate. Methods: 80 patients suspected aortic-diseases were divided into two groups randomly and underwent MSCT aortic-angiography with two different injection protocols respectively; i.e. group A (MSCT-64): 60 mL contrast material was injected followed by flushing with 40 mL saline solution; group B (MSCT-16): 70 mL contrast material was injected followed by flushing with 30 mL saline solution. The scanning delay time was adopted by the auto-trigger technique. Regions of interest were marked and their attenuation values were individually and respectively measured in the ascending aorta (AA), aortic arch, descending aorta (DA) in thoracic vertebra 7, lumbar 2, aortic artery forfication, two external iliac artery ending. The enhancement of arteries and the definition of the reconstructed vessels were evaluated respectively by two experienced doctors. The scan time (T), dose of contrast material (D), weighted CT dose index of volume (CTDIvol), z axis length (L), dose-length product (DLP) were recorded respectively and statistics analysis were performed with all data. Results: The average attenuation values by MSCT-64 and MSCT-16 in the ascending aorta (AA), aortic arch, descending aorta (DA) in thoracic vertebra 7, lumbar 2, aortic artery forfication were: 347.35, 350.32; the difference between the two groups was insignificant. The quality of reconstruction images and the manifestation of vessel branch between group A and group B was equal; The scan time of Group A and B: 7.12s, 24.98s; dose of contrast material of A and B: 60 mL, 70 mL, effective dose of A, B: 12.25 mSv, 14.64 mSv; the CTD Ivol of 64-slice spiral CT is 28.14% of 16-slice spiral CT. The difference of dose-length product is significant (p<0.01). Conclusion: There is fine consistence in vessel strengthening and manifestation of constructed vessel branch between 64-slice spiral CT and 16-slice spiral CT; The scan time shortened 71.50%, The dose of contrast material deplete 16.67%, Radiation dosage cut down 16.33%.