Pulmonary embolism cannot be detected by X-ray. Although in rare cases, some signs might appear on an X-ray, such as localized sparse lung markings, these signs are typically not characteristic. For conditions like pulmonary embolism, color Doppler ultrasound can be used to assist in diagnosis. If the ultrasound suggests deep vein thrombosis in the legs along with pulmonary hypertension, it indicates a high possibility of pulmonary embolism. Additionally, testing for D-dimer and blood gas analysis can also help in diagnosing pulmonary embolism. CT pulmonary angiography can also be used to diagnose the condition. CT and pulmonary angiography have a high diagnostic value for pulmonary embolism, and most cases can be definitively diagnosed through these tests.