The gold standard for the diagnosis of pulmonary embolism is DSA angiography of the pulmonary artery. Since DSA of the pulmonary artery is invasive, the non-invasive examination of CTA of the pulmonary artery is often used as the gold standard for diagnosis. Pulmonary artery CTA can clearly show whether there is pulmonary embolism in the main pulmonary artery and its branches. Many doctors use D-dimer in laboratory tests to determine whether a patient has pulmonary embolism, which is unreliable because D-dimer is mainly used for negative exclusion. If D-dimer is negative, pulmonary embolism can be ruled out by a rapid method, but a positive D-dimer is not diagnostic of pulmonary embolism, and it is not the gold standard for diagnosing pulmonary embolism, regardless of the high D-dimer value. Even if there are suspected symptoms of D-dimer, the presence of pulmonary embolism should be diagnosed by pulmonary CTA in combination with D-dimer.