Filling defect is a descriptive term in the imaging report, which needs to be determined according to what tests the patient has done. For example, if the patient has a CTA of the pulmonary artery and the report suggests a filling defect shadow in the pulmonary artery, pulmonary embolism is considered. A filling defect shadow in the pulmonary artery means that there is an embolus formation in the pulmonary artery, resulting in a filling defect in the lumen, and the pulmonary artery is not completely filled, which is called a filling defect. From there, the diagnostic report will suggest a pulmonary artery embolism and the physician will consider whether thrombolysis is needed depending on the patient’s condition. If there is a filling defect shadow in the head and neck vessels, it needs to be combined with the clinical history to consider intravascular plaque and sub-total occlusion of the vessels, which also shows a filling defect.