If pulmonary embolism cannot be detected by X-ray, clinical examination of pulmonary embolism can be done by pulmonary ECT, i.e. pulmonary nuclear scan or pulmonary CTA to check whether pulmonary embolism is present. If the patient has a severe pulmonary embolism, is already in coma or the patient is in poor physical condition and cannot undergo pulmonary CTA, the patient can be evaluated for the presence of pulmonary embolism based on cardiac ultrasound, electrocardiogram and blood D-dimer. For patients who can undergo pulmonary CTA, because pulmonary CTA can clarify the presence of thrombus in the main trunk and embolism in the branch pulmonary arteries, because the accuracy of pulmonary CTA can be more than 90%, invasive pulmonary DSA can also be performed.