Computed tomography angiography (CTA) is an accurate test for the detection of pulmonary embolism (PE) and is gaining increased acceptance as a fi rst-line study for diagnosing acute pulmonary embolism. Prompt and accurate diagnosis of PE is of great importance because treatment reduces mortality from 30% to < 10%. Recent advances in single-detector row helical CT pulmonary angiography include improvements in x-ray tube technology and faster gantry rotation, which allow for increased body coverage by using narrower collimation. These advances have been associated with an improved sensitivity and specifi city of the technique, from more than 80% to more than 90% in recent series. The most important advantage of CT over other imaging modalities is that both madiastinal and parenchymal structures can be evaluated, and thrombus can be directly visualized. Investigators have reported that subsegmental emboli can be missed; however, visualization of smaller arterial branches, and therefore detection of small emboli, have improved with the availability of multidetector scanners. PE being a pathologic condition causes both partial and complete intarluminal fi lling defects, which should have a sharp interfece with intravascular contrast material. In acute pulmonary embolism that manifestes as complete arterial occlusion, the aff ected artery may be enlarged. Partial fi lling defects due to acute pulmonary embolism are often centrally located, but when eccentrically located they form acute angles with the vessel wall. Some factors that cause misdiagnosis of pulmonary embolism may be patient-related, technical, anatomical or pathological. The radiologist needs to determine the quality of a CT pulmonary angiography study and whether pulmonary embolism is present. If the quality of the study is poor, the radiologist should identify which pulmonary arteries have been rendered indeterminate, and whether additional imaging is necessary. The aim of this study was to introduce the current views for diagnosing PE in CTA.