Computed Tomography scan

What is a CT or CAT scan?

ACR Radiology - Computed Tomography

A CT or CAT scan is a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called "slices"), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general x-rays. Our protocols are customized to each child to expose them to the minimal amount of radiation needed to obtain diagnostic images.

In computed tomography, the x-ray beam moves in a circle around the body. This allows many different views of the same organ or structure, and provides much greater detail. The x-ray information is sent to a computer that interprets the x-ray data and displays it in 2-dimensional form on a monitor.

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CT scans may be done with or without contrast. "Contrast" refers to a substance taken by mouth or injected into an intravenous (IV) line that causes the particular organ or tissue under study to be seen more clearly. Contrast examinations may require you to fast for a certain period of time before the procedure. Your physician will notify you of this prior to the procedure.

You will need to let your physician know if you have ever had a reaction to any contrast dye, or if you are allergic to iodine or seafood. If you are pregnant or think you may be pregnant, you should notify your physician. If you are claustrophobic or tend to become anxious easily, tell your physician ahead of time, as he/she may prescribe a mild sedative for you before the procedure to make you more comfortable. It will be necessary for you to remain still and quiet during the procedure, which may last 30 to 60 minutes.

Before your examination:

Tell the radiologist:

  • if you are allergic to iodine or other materials.
  • if you are pregnant.
  • if you are claustrophobic and think you will be unable to lie still while inside the scanning machine.

How is a CT or CAT scan performed?

CT scans can be performed on an outpatient basis, unless they are part of a patient's inpatient care. Although each hospital may have specific protocols in place, generally, CT scans follow this process:

  1. When the patient arrives for the CT scan, he/she will be asked to remove any clothing, jewelry, or other objects that may interfere with the scan.
  2. If the patient will be having a procedure done with contrast, an intravenous (IV) line will be started in the hand or arm for injection of the contrast medication. For oral contrast, the patient will be given medication to swallow.
  3. The patient lies on a scan table that slides into a large, circular opening of the scanning machine.
  4. The CT staff will be in another room where the scanner controls are located. However, the patient will be in constant sight of the staff through a window. Speakers inside the scanner will enable the staff to communicate with and hear the patient. The patient will have a call bell so that he/she can let the staff know if he/she has any problems during the procedure.
  5. As the scanner begins to rotate around the patient, low-dosage x-rays pass through the body for short amounts of time.
  6. The x-rays absorbed by the body's tissues are detected by the scanner and transmitted to the computer.
  7. The computer transforms the information into an image to be interpreted by the radiologist.
  8. It is very important that the patient remain very still during the procedure.
  9. The technologist will be watching the patient at all times and will be in constant communication.
  10. The patient may be asked to wait for a short period of time while the radiologist examines the scans to make sure they are clear. If the scans are not clear enough to obtain adequate information, the patient may need to have additional scans performed.

Preparing your child for a CT scan

You will receive detailed instructions about preparing your child for the scan. You also will receive a phone call on the day before the scan confirming the preparation instructions.

If your child will be receiving sedation please follow the instructions below:

  • No solid food eight hours before the scan
  • No milk or formula for six hours before the scan
  • No breast milk for four hours before the scan
  • No clear liquids for two hours before the scan

It is important that you follow these special instructions. If your child eats or drinks anything after the times listed above, the scan may be cancelled.

If your child has diabetes or is taking medicine, check with their doctor about these special instructions.

If you feel that your child is old enough to lie still and will not need sedation, but he or she is having a CT scan of the abdomen and pelvis, please follow these instructions:

  • Don’t let your child have anything to eat or drink within four hours before the scan. 
  • If you child does not feel well, it may be hard for him or her to lie still. If your child is sick on the day of the appointment, we may not be able to give your child sedation. Please call the CT department at (414) 266-3200. You may need to reschedule your child’s appointment.
  • Prepare your child for the possibility that he or she may be given contrast or other medicine through an IV.

Arrival instructions

If your child is having a CT scan of the abdomen and pelvis, please be at the hospital one hour before your appointment time. Your child will need to drink contrast mixed with a beverage before the scan.

For all other CT scans, please be at the hospital 30 minutes before your appointment time. Getting to the hospital early will give you time to register and ask questions. The CT nurse or technologist will be there to talk with you and your child.

Learn more about preparing for your child’s CT scan (PDF).