Radionuclide Cystogram (RNC)

What is a radionuclide cystogram?

A radionuclide cystogram, known as an RNC, is a diagnostic imaging exam that determines if your child has vesicoureteral reflux, which occurs when urine flows from the bladder back up into the kidneys. Technetium-99m is a radiopharmaceutical that is mixed with normal saline and is then instilled into your child’s bladder through the urethra. A special camera, called a gamma camera, is used to take pictures as the radiopharmaceutical fills the bladder. When the bladder is full, your child will be asked to void while the camera continues to take pictures.

An RNC can help:

  • diagnose reflux from the bladder to the kidneys
  • to follow-up on patients with known urinary reflux following antibiotics or anti-reflux surgery

How should I prepare my child for an RNC?

There is no special preparation needed for this test. Your child can eat or drink as usual. It is helpful to give your child a simple explanation as to why an RNC is needed and assure them that you will be with them for the entire time.

You may want to bring your child’s favorite book, toy or comforting object to use during waiting and imaging times.

What happens during an RNC?

Your child will be asked to lie on the imaging table. Girls will be asked to lie with their knees bent and dropped to the side with their feet together, in a "frog" position. Boys will be asked to lie with their legs straight.

Your child's genitalia region will be washed sterilely with soap and water using soft cotton balls. It is very important that this area stays extremely clean so not to introduce any bacteria to the area. A small amount of xylocaine jelly, which acts as a lubricant and numbing agent, will be placed at the urethra opening and on the tip of the catheter (small flexible plastic tube).

The technologist will gently slide the catheter through the urethra opening and into the bladder. The catheter will then be taped to hold it in place. Urine that is in the bladder will be collected for bacteriologic testing. The catheter will be connected to a bag of saline solution containing the radiopharmaceutical. Imaging will begin and the liquid will flow from the bag into the bladder. It is important that your child remains still during imaging to obtain the best quality images.

When your child's bladder is full, the catheter will be removed and your child will be asked to void into a plastic container. A potty chair may be used for older and cooperative patients.

The images will continue to take pictures for 20 minutes or until the bladder is empty. A post void image may be required if the bladder does not completely empty during the first phase of the study.

The entire test takes up to 30 minutes.

Will my child feel anything during an RNC?

Your child may feel discomfort with the placement of the catheter. Our personnel are aware of the sensitive nature of the area to be tested and every effort is made to ensure privacy and to make sure the patient is as comfortable as possible.

Is an RNC safe? 

Nuclear medicine has been used on babies and children for more than 40 years with no known adverse effects from the low doses employed. The radiopharmaceutical contains a very tiny amount of radioactive molecules, but we believe that the benefit to your child’s health outweighs potential radiation risk. The camera used to obtain the images does not produce any radiation. It is safe to be in the room with your child if you are pregnant or nursing

What happens after the RNC?

Once the RNC is complete, the images will be evaluated for quality. If the scan is adequate, your child will be free to leave and resume normal activity.

After the test, your child may have pink urine or feel some discomfort the next two or three times when going to the bathroom. Call your doctor if your child has blood in the urine, pain, fever or is unable to urinate after eight hours.

The nuclear medicine physician will provide a report to the doctor who ordered your child’s RNC. Your child’s doctor will then discuss the results with you.

How Boston Children’s Hospital approaches RNCs

The Nuclear Medicine and Molecular Imaging program at Children’s is committed to providing a safe, comfortable and child-friendly atmosphere with:

  • specialized nuclear medicine physicians with expertise in interpreting RNCs in children of all ages
  • certified nuclear medicine technologists with years of experience imaging children and teens
  • child life specialists to help families prior to and during exams
  • equipment adapted for pediatric use, which means age-appropriate care for children
  • protocols that keep radiation exposure as low as reasonably achievable while assuring high image quality