Abstract： Objective To explore the diagnostic values of dual energy lung perfusion in the diagnosis of pulmonary embolism by using dual-source CT (DSCT). Methods Thirty patients with clinically suspected pulmonary embolism underwent dual-energy scanning with dual-source CT. The scanned data were integrated into three groups including 140, 80 kV and coefficient of 0.3. According to the CT pulmonary angiography (CTPA) of the fusion data, the patients were divided into pulmonary embolism group and normal group. The thin-slice reconstruction of data was analyzed using dual-energy perfusion imaging analysis software. The lung field was divided into upper, middle and lower part to make quantitative analysis of lung tissue perfusion. Paired t-tests were used in the normal patients to compare bilateral lungs, and independent samples t-tests were applied to compare the embolism group and normal group, while minimum intensity projection images (MinIP) were utilized in the assessment of lung ventilation. Results Dual energy CT showed symmetrical homogeneous perfusion in 16 normal cases, without significant perfusion defects. Quantitative analysis showed that left and right lung perfusion were (27 ± 7) and (28 ± 8 ) HU respectively, and no significant difference was found between the two sides ( t=-1.73, P ＞0.05 ).Perfusion of the left upper, middle and lower lung was ( 23 ± 6), (24 ± 6), and (28 ± 8) HU respectively, while the perfusion of right upper, middle and lower lung was (26 ±8), (27 ±8), and (28 ±9) HU respectively, showing no statistical significant difference between the two sides (t=-1.91, -1.96,-1.73 ,P＞0.05 ). Angiography of pulmonary embolism group(14 cases)showed filling defects in the pulmonary trunk, segments and sub-segments. Pulmonary perfusion imaging showed low perfusion or defectsin lung field that dominated by embolic vessels. Quantitative analysis showed that the perfusion of the whole lung and the middle and lower lung were (22 ±5), (22 ±8), and (21 ±8) HU in the embolism group,which were significantly different from the normal group (t=-2. 10, -2.32, -2.63, P＜0.05).Minimum intensity projection images showed a good consistency of abnormal ventilation zone area and perfusion abnormalities. Conclusions Pulmonary perfusion status, especially pulmonary embolism, can be analyzed by dual energy CT scanning. It helps to early discover and precisely locate the embolism.