Objective   To study the diagnostic value of multislice spiral CT angiography (CTA) in the diagnosis and severity assessment of pulmonary embolism (PE).   Methods   Clinical and imaging data of 36 cases of PE admitted in our hospital during May 2005 to March 2009 were reviewed retrospectively. All patients underwent conventional CT scanning and CTA with 64-slice spiral CT or e-Speed electron beam CT scanning (GE Medical System

Milwaukee

WI). Axial section and some post-processed images

including maximum intensity projection (MIP)

multiplanar reconstruction (MPR)

volume rendering (VR) and virtual endoscopy (VE) were analyzed.   Results   In 36 cases of PE

2 070 branches of pulmonary artery were analyzed and PE was detected in 748 branches (36.1%). In 216 lobar arteries

PE was detected in 75 branches (34.7%)

in 720 segmental arteries PE was detected in 319 branches (43.3%)

and in 1 134 subsegmental arteries PE was detected in 354 branches (31.2%). Based on clinical manifestations the patients were classified into 2 groups

severe group and non-severe group. In 15 cases of severe group

pulmonary embolism index was (56.7±11.3)%

the central pulmonary artery was involved in 39 branches (43.3%)

and the right ventricle/left ventricle maximum minor axis ratio (RV∶LV ratio) 1.46±0.62. In 21 cases of non-severe group

pulmonary embolism index was (27.4±9.6)%

central pulmonary artery was involved in 36 branches (28.6%)

and the RV∶LV ratio was 1.06±0.35. The difference of the parameters between 2 groups was statistically significant (P0.05

0.01).   Conclusion   Multislice spiral CT angiography displays PE intuitively and determines its extent and severity. Our data suggest that pulmonary embolism index ＞40% can be used as the important criteria for the diagnosis of large area PE.