Usually, it is not necessary to hold urine for perfect ultrasound of the digestive system (liver, gallbladder) and renal ultrasound, and it is necessary to hold urine for ultrasound of the urinary system. Whether or not to hold urine has no effect on the image observation in ultrasound of the digestive system. However, in order to better understand the functional status of each organ, complete ultrasound of the digestive system (liver, gallbladder, pancreas, spleen) and kidney ultrasound requires fasting and water fasting for more than 8 hours. Fasting can reduce or even avoid the interference of ultrasound due to food or gas production in the gastrointestinal tract, and the gallbladder can also be in a state of bile filling, so that the acoustic image of each organ during the examination is clearer and clearer, and the results are guaranteed to be more accurate. Need to drink water to hold urine examination: perfect ureter, bladder, prostate, etc., need to drink more water to hold urine, the purpose is to make the bladder full, because urine is a good medium for ultrasound through, so that they can more clearly see whether there is any abnormal lesions.