What It Is

A voiding cystourethrogram (VCUG) uses a small amount of radiation to make images of a person's urinary system.

After the patient's bladder is filled with a liquid called contrast material, an X-ray machine sends beams of radiation through the abdomen and pelvis, and images are recorded on special film or a computer. These images help doctors see problems in parts of the urinary system, including the bladder, urethra (the tube connecting the bladder with the outside of the body), and the ureters (the tubes connecting the kidneys to the bladder).

X-ray images are black and white. Dense body parts that block the passage of the X-ray beam through the body, such as bones, appear white on the X-ray image. Contrast material also appears white, and when it fills the organs of the urinary system, it makes them visible. Softer body tissues, such as the skin and muscles, allow the X-ray beams to pass through them and appear darker. Air in the stomach and intestines appears black.

An X-ray technician or radiologist takes the X-rays using a technique called fluoroscopy. While the contrast material fills your child's bladder, and then while your child empties the bladder, the technician or radiologist watches an onscreen X-ray video of the liquid moving through the urinary system and a series of X-ray films is recorded.

Why It's Done

A VCUG can check for problems in the structure or function of the urinary system. It can evaluate the bladder's size and shape and look for abnormalities, such as a blockage along the path of the urine.

It also can show whether the urine is moving in the right direction. Normally, urine flows from the kidneys down to the bladder through the ureters. When urine goes back up toward the kidneys, it's called vesicoureteral (VU) reflux, which a VCUG can detect. Sometimes VU reflux only occurs while urinating (voiding), which is why the VCUG includes taking X-ray images while the bladder is being emptied.

Since VU reflux can cause urinary tract infections (UTIs), this test is sometimes recommended after a child has had a UTI. Although not all kids who have had UTIs have reflux, it's important to find those who do, since the treatment may vary depending on the severity of reflux.