A voiding cystourethrogram (VCUG) is a special type of x-ray called a fluoroscopy to study the bladder and urethra. Contrast medium is injected through a catheter that is inserted through the urethra into the bladder. Once the bladder is filled the radiologist will remove the catheter. X-ray images will be taken while the bladder is full and as you empty it to look for any problems with the bladder and urethra.

Normally the kidneys produce urine and move it through the ureters into the bladder. When the bladder is full, a mechanism prevents urine from flowing back into the kidneys and instead moving it through the urethra. The backflow of urine is called the vesicoureteral (VU) reflux. It occurs due to problems with the valves or ureters. If mild, urine flows back to the lower ureters; if severe, urine can travel back to the kidneys and case them to swell. In some children this problem may be congenital.