Fasting is required for liver, bile, spleen and kidney examinations together. Strictly speaking, fasting is required for liver and bile, and fasting is not required for ultrasound examinations of spleen and kidney alone, and fasting or not fasting has no effect on their ultrasound results. In addition to the liver and biliary tract, there are also ultrasound examinations of the pancreas, gastrointestinal tract, abdominal vessels, and adrenal glands, etc. The reasons for fasting are: 1. Total reflection leads to serious attenuation of acoustic energy, and the deep structure of the gas is not displayed, which affects the display of ultrasound images of the liver, pancreas, adrenal glands and abdominal vessels. Therefore, for ultrasound examination of these areas, it is usually necessary to fast for more than eight hours.