It is not necessary to hold urine to do ultrasound of liver, gallbladder, spleen, pancreas and kidney, but only when doing ultrasound of pelvic organs. Because the organs in the pelvic cavity, such as ureter, uterus, fallopian tubes, ovaries and prostate, are located behind the bladder or small intestine, only after filling the bladder by holding urine and improving the resolution of the organs behind the bladder, can the organs in the pelvic cavity be clearly displayed. If urine is not held, the gas in the bladder or small intestine will absorb the ultrasound, making it impossible for the ultrasound to reach the organs that need to be examined in the pelvis, affecting the diagnosis of these organs.