(1) Fasting from food and water for 4 hours. (2) Hypotension: Intramuscular injection of 654-2 20mg 5-10 minutes before the examination. (3) Gastric filling: Negative contrast agents: milk, water, gas. At present, drinking water is generally used as a contrast agent. Foreign scholars advocate drinking 500~800ml of water, domestic advocates 1000~1200ml, at least 800ml. generally after hypotension, 5~10min before CT examination once or in 2 times, drink water as fast as possible and avoid swallowing gas. Objective: to make the stomach fully relaxed and dilated and delay emptying; to reduce gastric peristalsis and eliminate artifacts; to reduce gastric peristalsis and eliminate pseudo-thickening of the gastric wall. Some scholars believe that gas filling is better: oral gas-producing agent 3~6 g. Positive contrast agent (0.5~1% iodine water) is rarely applied at present. (4) Respiratory training: the patient is trained to breathe before the scan to cooperate with the examination in order to improve image quality and prevent missing small lesions.