Abstract: Objective To investigate the feasibility of low concentration contrast agent combined double low dose in CT pulmonary angiography. Methods60 patients with clinically suspected pulmonary embolism examed by CT pulmonary angiography (CTPA) were divided into two groups (experimental group: n=30, 80 kV, 15 mL, 320 mg I/mL;control group: n=30, 120 kV, 50 mL, 370 mg I/mL). The average CT value of main right and left pulmonary arteries, lobar arteries was calculated. Imaging post processing techniques included curved plannar reconstruction (CPR), volume rendering (VR) and maximal intensity projection (MIP). The artifact of the remaining contract in the superior vena cava and overall quality of the image were observed and analyzed by two senior doctors who were double blinded. ResultsAll patients in two groups completed CTPA successfully. The image qualities of two groupssatisfy clinical diagnostic requirements and no difference of the image qualities was observed between two groups (P>0.05). The evaluation of venous pollution in experimental group was better than that of control group (P<0.01).No difference of CT values were observed between two groups 〔experimental group (423.2±89.4) HU, control group (465.7±85.6) HU〕(P>0.05). The SNR and CNR in experimental group were lower than those in control group (P<0.01 both).The CT dose index volume (CTDIvol)， dose-length product (DLP) and size-specific dose estimates (SSDE) in experimental group were significantly lower than those incontrol group (P<0.01 all). ConclusionThe low concentration contrast agent combined double low dose in CT pulmonary angiography satisfies clinical diagnostic requirements. It has good clinical value for it could reduce venous pollution, iodine contrast agent and radiation exposure.