Children's (Pediatric) Computed Tomography

What is a CT scan?

CT scanning, sometimes called CAT scanning, is a noninvasive medical test that helps physicians diagnose and treat medical conditions. CT imaging combines special x-ray equipment with sophisticated computers to produce multiple images or pictures of the inside of the body. These cross-sectional images of the area being studied can then be examined on a computer monitor or printed. CT scans of internal organs, bone, soft tissue and blood vessels provide greater clarity and reveal more details than regular x-ray exams.

Newborns, infants and older children may undergo CT scanning.

What are some common uses of the procedure?  

Physicians use the CT examination to help detect a wide range of abnormalities and disease, including cancer, in any part of a child’s body. Children’s (pediatric) CT is typically used to help diagnose and monitor treatment for infectious or inflammatory disorders, abdominal pain, headaches and injury-related changes.

CT is also performed to evaluate:

  • blood vessels serving the brain, face or neck
  • the spinal cord and bones making up the spinal column

In the case of head injury, the exam can display or rule out serious complications such as bleeding within the brain or other forms of brain damage. Except for the chest x-ray, CT is the most commonly used imaging procedure for evaluating the chest. CT of the chest is used to evaluate:

  • complications from infections such as pneumonia
  • a tumor that arises in the lung or has spread there from a distant site
  • airway disease such as inflammation of the bronchi (breathing passages)
  • birth defects
  • injured blood vessels or lung damage

Using multidetector CT, it is possible to obtain very detailed pictures of the heart and large blood vessels of the chest in children, even newborn infants.

CT is well-suited for visualizing diseases or injury of important organs in the abdomen including the liver, kidney and spleen. CT is sometimes used to:

  • diagnose appendicitis
  • evaluate adolescents who have inflammatory disorders of the bowel, such as colitis
  • detect abdominal tumors or birth defects

In the pelvic region, CT scans can help detect:

  • cysts or tumors of the ovary
  • abnormalities of the bladder
  • stones in the urinary tract
  • disease of the pelvic bones

How should we prepare?

Your child should wear comfortable, loose-fitting clothing to the exam. He or she may be given a gown to wear during the procedure. Metal objects including jewelry, eyeglasses, removable dental work, hearing aids and hairpins may affect the CT images and should be left at home or removed prior to your child’s exam. Your child may be asked not to eat or drink anything for several hours beforehand, especially if a contrast material, sedative or anesthesia will be used in the exam. With sedation or anesthesia, your child probably will not be allowed to eat for three to six hours prior to the exam. In general, children who have recently been ill are not sedated or anesthetized. If this is the case or if you suspect that your child may be getting sick, you should talk with your physician about rescheduling the CT exam.

You should also inform your physician of any medications your child is taking and if he/she has any allergies, especially to contrast materials, iodine, or seafood. Also inform your doctor of any recent illnesses or other medical conditions your child may have, and if there is a history of heart disease, asthma, diabetes, kidney disease or thyroid problems. Any of these conditions may increase the risk of an allergic reaction.

What does the equipment look like?

The CT scanner is typically a large machine with a hole, or tunnel, in the center. A moveable examination table slides into and out of this tunnel. In the center of the machine, the x-ray tube and electronic x-ray detectors are located opposite each other on a ring, called a gantry, which rotates around the patient. The computer that processes the imaging information and monitor are located in a separate room.

How does the procedure work?

In many ways CT scanning works very much like other x-ray examinations. X-rays are a form of radiation-like light or radio waves-that can be directed at the body. Different body parts absorb the x-rays in varying degrees. In a conventional x-ray exam, a small burst of radiation is aimed at and passes through the body, recording an image on photographic film or a special image recording plate. Bones appear white on the x-ray; soft tissue shows up in shades of gray and air appears black.

With CT scanning, numerous x-ray beams and a set of electronic x-ray detectors rotate around the patient, measuring the amount of radiation being absorbed throughout the body. At the same time, the examination table is moving through the scanner, so that the x-ray beam follows a spiral path. A special computer program processes this series of pictures, or slices of the body, to create two-dimensional cross-sectional images, which are then displayed on a monitor.

CT imaging is sometimes compared to looking into a loaf of bread by cutting the loaf into thin slices. When the image slices are reassembled by computer software, the result is a very detailed multidimensional view of the body’s interior. Refinements in detector technology allow new CT scanners to obtain multiple slices in a single rotation. These scanners, called “multislice CT” or “multidetector CT,” allow thinner slices to be obtained in a shorter period of time, resulting in more detail and additional view capability. Modern CT scanners are so fast that they can scan through large sections of the body in just a few seconds. Such speed is beneficial for all patients but especially children, the elderly and critically ill.

For some CT exams, a contrast material is used to enhance visibility in the area of the body being studied.

How is the procedure performed?

The technologist begins by positioning the patient on the CT examination table, usually lying flat on his/her back or possibly on their side or on their stomach. Straps and pillows may be used to help the patient maintain the correct position and to hold still during the exam. You should encourage your child to report any discomfort during positioning because it is important to keep very still during the exam. Once the child is correctly positioned, the CT technologist will leave the room to begin the scan.

If contrast material is used, it will be swallowed, injected through an intravenous line (IV) or administered by enema, depending on the type of examination. Next, the table will move quickly through the scanner to determine the correct starting position for the scans. Then, the table will move slowly through the machine as the actual CT scanning is performed. Patients are periodically asked to hold their breath during the scanning.

Most children older than six years are able to hold their breath long enough to complete the scan although they may need coaching and practice. Younger children may not be able to hold their breath long enough to complete the scan. Irregular breathing can affect the quality of a CT scan, especially one done to evaluate the chest or upper abdomen. It is often better to have young children breathe quietly and regularly during the scan. Modern systems known as multidetector or multislice CT are able to image large regions of the body in a very short time.

When the examination is completed, the patient will be asked to wait until the technologist determines that the images are of high enough quality for the radiologist to read.

What will my child experience during and after the procedure?

Most CT exams are painless, fast and easy. With helical CT, the amount of time that the patient needs to lie still is reduced. Though the scanning itself causes no pain, your child may experience some discomfort from having to remain still for several minutes.

If an intravenous contrast material is used, your child will feel a slight pin prick when the needle is inserted into a vein in the hand or arm. The child may have a warm, flushed sensation during the injection of the contrast materials and a metallic taste in his/her mouth that lasts for a few minutes. Occasionally, a patient will develop itching and hives, which can be relieved with medication. If your child becomes light-headed or experiences difficulty breathing, you should notify the technologist or nurse, as it may indicate a more severe allergic reaction.

If the contrast material is swallowed, your child may find the taste mildly unpleasant; however, most patients can easily tolerate it. Your child can expect to experience a sense of abdominal fullness and an increasing need to expel the liquid if the contrast material is given by enema. In this case, encourage your child to be patient, as the mild discomfort will not last long.

When your child enters the scanner, special lights may be used to ensure that he/she is properly positioned. With modern CT scanners, your child will hear only slight buzzing, clicking and whirring sounds as the CT scanner revolves around him/her during the imaging process. Your child will be alone in the exam room during the CT scan, however, the technologist will be able to see, hear and speak with him/her at all times. A parent may be allowed in the room but will be required to wear a lead apron to prevent radiation exposure. If you suspect you may be pregnant it would be better for someone else to be with your child.

Some imaging facilities may use general anesthesia in young children who are unable to hold still. In this case you will be permitted to stay in the exam room until your child has fallen asleep. There may be a somewhat longer wait after the exam to be sure that your child is fully alert. When the exam is completed and your child-if sedated-is fully awake, you will be free to return home. After a CT exam, your child can return to his/her normal activities. If a contrast material was used during the exam, you will be given special instructions.

Who interprets the results and how do we get them?

A physician, usually a radiologist with expertise in supervising and interpreting radiology examinations, will analyze the images and send a signed report to your primary care or referring physician, who will discuss the results with you.

What are the benefits vs. risks?

Benefits

  • Using a spiral (helical) CT unit to examine children is faster than the older CT scanners, reducing the need for sedation and general anesthesia.
  • New technologies that will make even faster scanning possible are becoming increasingly available. For children this means shorter imaging times and less time required to hold still in order to produce clear images. Also, shorter scan times will make it easier for children to hold their breath during critical parts of the exam.
  • CT scanning is painless, noninvasive and accurate.
  • A major advantage of CT is that it is able to image bone, soft tissue and blood vessels all at the same time.
  • Unlike conventional x-rays, CT scanning provides very detailed images of many types of tissue as well as the lungs, bones, and blood vessels.
  • CT examinations are fast and simple; in emergency cases, they can reveal internal injuries and bleeding quickly enough to help save lives.
  • CT has been shown to be a cost-effective imaging tool for a wide range of clinical problems.
  • CT is less sensitive to patient movement than MRI.
  • CT can be performed if you have an implanted medical device of any kind, unlike MRI.
  • CT imaging provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies and needle aspirations of many areas of the body, particularly the lungs, abdomen, pelvis and bones.
  • A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy.
  • No radiation remains in a patient’s body after a CT examination.
  • X-rays used in CT scans usually have no side effects.

Risks

  • There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
  • The risk of serious allergic reaction to contrast materials that contain iodine is rare, and radiology departments are well-equipped to deal with them.

Radiation is necessary to obtain CT images. It is known that high levels of radiation may cause cancer. However, CT scans result in a low-level exposure. Whether such levels cause cancer is debatable but because it is possible, every effort is made to limit the amount of radiation children may receive from a CT scan. The thyroid gland, bone marrow and gonads of a child are especially sensitive to radiation. In addition, children have a longer time to accumulate radiation throughout their lives. Each exposure, including that from a CT exam, adds to this total lifetime exposure.

One of the best ways of limiting radiation exposure is to avoid CT scans that are not clearly needed. Other measures are to restrict the area scanned as much as possible and to “fine tune” the CT settings based on the reason for the exam, the body area being examined, and the child’s size. Radiologists generally attempt to use the lowest radiation dose that will provide the needed diagnostic information.

  • There always is a risk of complications from general anesthesia or sedation. Every measure will be taken to protect the welfare of your child, including close monitoring.
  • Children should have a CT study only if it is essential for making a diagnosis and should not have repeated CT studies unless absolutely necessary.

What are the limitations of a child's CT?

A person who is very large may not fit into the opening of a conventional CT scanner or may be over the weight limit for the moving table. Other imaging methods such as ultrasound or MRI imaging can provide pictures of certain areas of the body that sometimes are as good as or better than those obtained by CT scanning. Working together, your primary care physician or pediatrician and the radiologist will decide which type of examination is best for your child.

Motion can affect the quality of a CT scan even when every effort is made to see that your child holds still.