Pulmonary embolism is a serious and potentially fatal condition affecting a large number of individuals annually. A missed or delayed diagnosis results in a large number of deaths annually due to untreated pulmonary embolism. At this study we explained the physics of spiral CT and the manifestations of pulmonary embolism as it appear with CT, with comparison between CT and other imaging modalities. We concluded that spiral CT is an accurate and cost effective, safe imaging modality for the diagnosis of pulmonary embolism thus it is expected to play a more significant role in the diagnosis of pulmonary embolism.