Abstract: Objective To investigate the effect of iodine flow rate (iodine flow quantity in unit time) on pulmonary angiography in multi-slice computed tomography (CT), and to guide the optimal use of contrast material. Methods From September 2010 to December 2011 in Shandong Medical Imaging Research Institute, 121 patients without significant pulmonary diseases were performed thorax enhanced CT scan, 40 patients were selected from them (81 cases with cardiac failure, pulmonary hypertension, pulmonary embolism, stenosis, pulmonary significant variation, deformity, or disagreement with the examination were excluded). Forty patients were randomly assigned to two groups (group A and group B, each group including 20 patients). The patients of group A were administrated intravenously 80 ml of 300 mg I/ml at a flow rate of 4.0 ml/s, and the group B were 60 ml of 400 mg I/ml at 3.0 ml/s followed by 20 ml saline at the same flow rate. All patients underwent dynamic scanning at the same pulmonary artery level. The pulmonary arterial peak time (PT), peak value (PV), the beginning time of more than 200 HU (Tb200) and duration time (T200) were analyzed according to time-dose curve (TDC). Results The peak value of pulmonary artery of group A and group B were (372.45±58.60) HU and (398.45±84.80) HU, respectively. There was no significant difference between them (t=1.044, P>0.05). The PT, Tb200 and T200 of group A was (19.90±2.63) s, (8.80±1.61) s, (19.95±4.65) s, and those of group B was (25.00±2.58) s, (14.31±4.42) s, (16.08±2.75) s with significant difference between group A and group B (t=5.490, 5.108, 2.702;P<0.05). Conclusion Using higher concentration contrast material, the dose and injected rate should be decreased appropriately, and the image quality was not weaken. Therefore, the higher concentrations of the contrast agent should be used in MSCT pulmonary angiography examination in practice.