Computed Tomography (CT or CAT) Scan

CT (computed tomography) is a non-invasive procedure that uses x-ray equipment and powerful computers to create detailed, cross-sectional images of your child's body. Most CT scans are performed in seconds, although it can take 10 minutes or longer to position the child correctly for the exam. A CT scan can provide more detailed images of bone, tissue, and blood vessels than conventional x-rays, and often is the imaging modality of choice during emergencies, because it provides vital information quickly.

The CT scanner itself is a large machine that looks like a giant doughnut. Your child will lie still on a table that slides into and out of the opening while the machine takes pictures of the part of their body that is being investigated. Even though the machine is large and makes humming noises, it will not touch your child during the scan.

An x-ray tube on a rotating gantry within the "doughnut" emits controlled, narrow beams of x-ray radiation, which pass through the body and get picked up by an array of electronic detectors on the frame's opposite side. This produces many pictures in thin two-dimensional "slices" of the area under study. The slices are then assembled by a dedicated computer, which can if necessary compile them into detailed three-dimensional images that can be studied from all angles.

In children, CT is often used to investigate head injuries or acute neurological symptoms, evaluate chronic sinus symptoms or hearing loss, diagnose appendicitis, evaluate masses, detect fractures, or help determine why a child has trouble breathing. Because it provides detailed views of many types of tissues, it's an excellent way to rule out disease and facilitate treatment.

Your child's doctor may have requested a CT scan to obtain specific diagnostic information that is not provided by or is complementary to other imaging technologies such as x-ray, ultrasound, nuclear medicine, or magnetic resonance imaging (MRI).

In emergencies, a CT scan can quickly reveal internal injuries and bleeding, providing important information to the medical team that may prove life-saving.

The most important thing is to tell your child in simple terms why the test is necessary. You can explain that the CT won't hurt and that the machine does not touch the body. If an IV is needed for the injection of contrast (the "dye" used to provide additional detail for some scans) or to provide anesthesia, your child may well feel discomfort from the needle. An option that is available for IV insertion is called a J-tip. A J-tip is used to numb the area before needle insertion. It is a syringe that has no needle but makes a popping sound to numb the area, similar to a can of soda being opened. The staff will give specific instructions when your exam is scheduled, but here are some general guidelines for CT scans without anesthesia:

• Notify the CT staff of any illness your child has, such as cold, cough, fever, diarrhea, or vomiting; we may need to reschedule the test.
• Tell us about all allergies or any previous drug reaction that may keep your child from receiving the contrast safely.
• If you have severe kidney disease or are on kidney dialysis, there is a risk of a condition called nephrogenic systemic fibrosis from the dye. You should discuss this risk with your child’s clinician prior to the test.
• Dress your child in comfortable clothing with no metal snaps, belt buckles, or zippers. In the case of CT scans of the head, metal hair clips and jewelry must be removed.
• If your child will need an intravenous or oral contrast agent, there are no specific dietary restrictions for most patients.

Because CT scans are generally quick — often less than 10 seconds — many children can hold still for the procedure. But depending on which part of the body is being scanned, the exam can take longer. Some types of scans are more forgiving of slight movements, while others require your child to be entirely motionless for a greater length of time. Depending on your child's age and other factors, anesthesia may be necessary. Our Try Without Anesthesia appointments offer patients of all ages the opportunity to try their CT scan without anesthesia, when applicable.

If your child is having an abdominal scan, you'll need to arrive two hours before the exam because your child will probably have to drink a contrast solution that will enhance the detail of the CT images. They may also need an IV-administered contrast, which is given by a technologist just before the exam.

After you have checked in, a technologist will greet you and explain the test in detail, answering any questions you or your child might have.

The technologist positions and secures your child on the movable bed that slides into and out of the CT scanner. At this point, the technologist may use a small needle to place an intravenous line into your child's hand or foot. There will likely be some brief discomfort when this is done.

The technologist then performs the exam according to the imaging protocol specified by the radiologist who is in direct contact with the radiologist at all times.

Having a parent in the room during the exam can help reduce any anxiety your child might have. However, you cannot be in the room if you are pregnant. In this situation, please bring the other parent or a trusted caregiver.

After the pediatric radiologist or pediatric neuroradiologist interprets the images, they will provide a written report to your child's doctor, who can then tell you the results. Results are typically reported within 24 hours. In urgent cases, radiologists communicate immediately with the referring physician.

CT scans involve ionizing radiation as is used in conventional x-rays. In certain clinical situations, the benefits of an accurate diagnosis outweigh the risk of exposure to radiation during the exam. We calibrate our x-ray-based equipment and adapt protocols to deliver doses appropriate to children. The narrow beams of radiation used in CT, as well as protective shielding that prevents unnecessary radiation to sensitive tissues, also help limit radiation dose.

Sometimes, it is possible to reach a diagnosis by using imaging technologies that do not involve radiation: ultrasound or magnetic resonance imaging (MRI), for example. When appropriate, our radiologists will advise referring physicians that this is the safest course of action.

Boston Children's Hospital is dedicated to putting children of all ages at ease, as you'll see from the whimsical décor of our Fenway Park and beach-themed CT rooms in Boston and our skilled and child-centered staff at all locations. We are experts at keeping children comfortable and we encourage parents to be in the room during the scan. In addition, our powerful multidetector scanners minimize exam time, often eliminating the need to sedate your child.

Because CT technology uses ionizing radiation, we adapt our equipment and protocols to keep doses "child-sized." We work hard to keep doses as low as possible without compromising the image quality needed to make a correct diagnosis.