If the patient is doing a CT scan of the head, neck, chest or bones of the extremities, fasting is not required, the patient can just scan normally, but if the patient is doing a CT scan of the abdomen, fasting is required, such as liver, spleen, gallbladder, pancreas, kidney and gynecological examinations. The purpose of fasting: on the one hand, it is for bile filling, which can better show the lesions of the gallbladder; on the other hand, it can avoid the interference of the gastrointestinal tract contents and gas to the surrounding organs, so as not to produce artifacts that can lead to misdiagnosis, etc.