In order to get the best results from ultrasound examinations, doctors often instruct patients to fast or hold urine before the examination. So, under what circumstances do you need to fast or hold urine? Examination of the gastrointestinal tract: The gastrointestinal tract often contains a large amount of gas, people eat with the swallowing of food can be sent to the gastrointestinal tract along with a large amount of gas, in addition to certain foods in the digestion process can also produce more gas, such as milk, beans, etc.. These gases can interfere with the passage of ultrasound and affect the clarity of the image, which can easily cause misdiagnosis or missed diagnosis. Examination of the gallbladder: The physiological function of the gallbladder is to store bile, and under normal circumstances the gallbladder will contract after a person eats fatty foods and expel bile. When the bile in the gallbladder decreases, it is not easy to see the lesions on the wall of the gallbladder clearly during ultrasound examination. Therefore, doctors often instruct patients to eat light, low-fat, non-gas-producing foods for dinner the day before the abdominal ultrasound examination, with the aim of minimizing gas in the gastrointestinal tract, while allowing the gallbladder to fill up sufficiently to minimize interfering factors and obtain the best images to improve the diagnosis rate. As with the examination of the gallbladder, holding the urine to fill the bladder allows the bladder wall to show more clearly. Holding the urine is not only for the examination of the bladder, but because the uterus, ovaries, prostate and other organs are located in a lower, deeper position in the pelvis below the back of the bladder and covered by a large number of intestinal tubes above its front, it is difficult for ultrasound to penetrate the gas in the intestines to reach these organs. The urine-filled bladder, however, can effectively push away the intestinal tubes occupying the pelvic cavity, overcoming the interference of intestinal gas and elevating the position of these organs so that they are clearly visible. It is important to note that we should not perform ultrasound reluctantly when we are not well prepared as mentioned above. If we are not prepared as required, the images of the organs are not clear, which may result in misdiagnosis, missed diagnosis, or even delayed treatment of the disease, which in turn may cause you considerable inconvenience.