Depending on the type of ultrasound examination you are having, you may be asked to perform a specific prep.
You will be asked to fill your bladder for these tests. You will be asked to drink at least 32 oz. of fluid one hour prior to the examination and not go to the restroom until the exam is complete. The reason for this prep is that a full bladder provides a fluid filled window into the pelvis by pushing the bowel up and allowing the pelvic organs to be visualized. Ultrasound passes easily through the fluid in the bladder but does not penetrate the bowel due to its high air content.
ABDOMINAL, GALLBLADDER, AORTA, KIDNEY, ABDOMINAL VASCULATURE
You will be asked not to eat or drink anything eight hours prior to your examination. By not eating, you will reduce the amount of air in your intestines. Ultrasound does not penetrate the bowel well due to its high air content. If necessary, you may take your regular medicines with a small sip of water.