The most important advantage of CT over other imaging modalities is that both mediastinal and parenchymal structures are evaluated, and thrombus is directly visualized. Studies have shown that up to two thirds of patients with an initial suspicion of PE receive another diagnosis, some with life threatening diseases, such as aortic dissection, pneumonia, lung cancer and pneumothorax. Most of these diagnoses are amenable to CT visualization, so that in many cases a specific etiology for the patient's symptoms and important additional diagnosis can be established.