A renal sonogram entails filling the bladder by drinking 24 ounces of water in the hour before the test, removing clothing and putting on a gown, lying on an exam table on the stomach, having a gel spread over the back and having an ultrasound transducer rubbed over the kidney area where the gel was applied, according to Johns Hopkins Medicine. The transducer is noninvasive and sends sound waves through the body tissues to provide a picture of the kidneys.
A renal sonogram provides health care workers with a picture of the kidneys by converting the sound waves that are bounced off the kidneys into a picture on a screen, states Johns Hopkins Medicine. Because sound waves move through different substances at different rates, the sonogram gives detailed information about the structure and location of the kidneys, and the blood flow through them. The gel allows the transducer to move smoothly over the skin making the procedure more comfortable and providing better contact for transmitting the sound waves.
Renal sonograms help diagnose cysts, tumors, abscesses, fluid retention and infections in the kidneys, ureters and bladder, according to Johns Hopkins Medicine. They also show kidney stones. Occasionally the technician needs to re-examine the renal structures after the patient empties his bladder at the end of the initial procedure.