In general, abdominal ultrasound requires an empty stomach and is best performed after a bowel movement. It is also best to eat a light diet with little oil the day before. Other system examinations such as thyroid, breast, heart, blood vessels, etc. do not require fasting. In general, the examination of digestive system, such as stomach, liver, gallbladder, pancreas, spleen and large blood vessels in the abdomen, requires fasting. This is because after eating will cause contraction of the gallbladder and bile ducts, resulting in reduction of gallbladder volume, thickening of the gallbladder wall, and poor display of the gallbladder wall and gallbladder lumen, resulting in unclear display of lesions in the gallbladder and bile ducts, making it difficult to make a clear diagnosis of the disease. Moreover, after eating, stomach contents and gas in the gastrointestinal tract can interfere with the display of some sections of the liver and the gallbladder and bile duct system, resulting in obscured or poorly displayed sonograms. Unlike other imaging examinations, ultrasound is very susceptible to gas interference, which may even make the examination impossible to perform. Therefore, for some patients, it is also necessary to perform an enema and bowel movement before performing the examination. For patients who need X-ray gastrointestinal imaging, it is necessary to arrange for color ultrasound examination first, and then barium X-ray meal examination, because barium will also prevent the penetration of ultrasound, so you should try to arrange for color ultrasound examination first, and then go for other examinations. Except for the abdominal examination which requires fasting, other examinations such as heart, blood vessels, thyroid, breast and both kidneys do not require fasting preparation. However, some of the lower abdominal and pelvic exams require holding urine.