CTA examination precautions: First, the examination requires the injection of contrast agent, which may cause allergic reactions. Therefore, before doing the examination, patients will be asked in detail about their clinical history and allergy history, such as whether there is severe hyperthyroidism or allergy to iodine contrast agent. If there are these two conditions, CTA examination should not be done. Secondly, if the patient’s liver and kidney function is not good, cardiac circulatory function is not good, long-term poor health, need to be done with caution, because the contrast agent may increase the toxicity of the kidneys. Fasting is required before doing CTA examination, and no eating is allowed. Patients taking metformin medication need to stop taking the medication for 48 hours before doing the test, and patients can’t do barium meal contrast in the last two weeks.