Not all ultrasound need to hold urine, usually only urology, gynecology, pelvic ultrasound need to hold urine, the examination need to hold urine to the extent that the bladder is full with the desire to urinate is appropriate. Usually, the examination of the heart, thyroid, liver, gallbladder, pancreas, spleen and other parts of the ultrasound is not required to hold urine, but the gallbladder ultrasound usually need to fasting examination. While urology, gynecology, pelvic-related ultrasound need to hold urine for examination, in order to help hold open the inside of the bladder and see the lesions inside the bladder clearly. In general, the degree of holding urine is in the bladder full with urgency to urinate, but press the abdomen will not appear incontinence is appropriate, to achieve this degree can better observe the overall structure of the urinary system. In addition, if some patients are unable to hold their urine, and a small amount of fluid in the bladder is intolerable, the bladder can be filled with fluid after catheterization under the operation of the doctor, and then examined. Patients who require this are advised to do so under the supervision of a physician.