PET / CT side effects are very small, side effects mainly from the radioactive nuclear elements, common for allergies. PET/CT examination itself belongs to non-invasive examination, except for the injection of contrast agent, there will be no other invasive, its side effects are still mainly from the radiation of radioactive nuclear elements, is the tracer used in the examination, the common side effect is allergy, to be used under the guidance of the doctor. Clinically used drug is 18F-FDG, which refers to fluorodeoxyglucose, radiation dose is very small, within the acceptable safety range of the human body, the impact is very small, and the decay and excretion is extremely fast, drink plenty of water after the examination can soon be excreted, but because it will be metabolized by the kidneys, so people with poor renal function is recommended to follow the doctor’s advice or not to do.