CT Scan

What is a CT Scan?
CT (computed tomography), sometimes called CAT scan, uses special X-ray equipment to obtain images from different angles around the body. Then a computer processes the information to show a cross-section of body tissues and organs.

CT imaging is particularly useful because it can show several types of tissue -- lung, bone, soft tissue and blood vessels -- with great clarity. Radiologists interpret CT scans of the body to more easily diagnose problems such as cancers, cardiovascular disease, infectious disease, trauma and musculoskeletal disorders. And because it provides detailed, cross-sectional views of all types of tissue, CT is especially effective for studying the chest and abdomen.

How should I prepare for the CAT scan?
You should wear comfortable, loose-fitting clothing for your CT exam. Metal objects can affect the image, so avoid clothing with zippers and snaps. You may also be asked to remove hairpins, jewelry, eyeglasses, hearing aids and any removable dental work, depending on the part of the body that is being scanned. You may be asked not to eat or drink anything for one or more hours before the exam. Women should always inform their doctor or x-ray technologist if there is any possibility they are pregnant.

How is the CAT scan performed?
CT scanning causes no pain, and today's faster scanners reduce the need to lie still for any length of time. The technologist begins by positioning the patient on the CT table. The patient's body may be supported by pillows to help hold it still and in the proper position during the scan. As the study proceeds, the table will move slowly into the CT scanner. Depending on the area of the body being examined, the increments of movement may be so small that they are almost undetectable or large enough that the patient feels the sensation of motion.

An X-ray tube inside the machine rotates around your body and sends small doses of radiation through it at various angles. As X-rays pass through your body, different tissues absorb different amounts. Detectors inside the machine measure the radiation leaving your body and convert the radiation into electrical signals. A computer gathers these signals and assigns them a color ranging from black to white depending on signal intensity. The computer then assembles the images and displays them on a computer monitor.

A CT examination often requires the use of different contrast materials to enhance the visibility of certain tissues or blood vessels. The contrast material may be swallowed, injected through an IV directly into the blood stream or administered by enema, depending on the type of examination. Before administering the contrast material, the radiologist or technologist may ask whether the patient has any allergies, especially to medications or iodine, and whether the patient has a history of diabetes, asthma, a heart condition, kidney problems or thyroid conditions. These conditions may indicate a higher risk of reaction to the contrast material or potential problems eliminating the material from the patient's system after the exam.

A CT examination usually takes five minutes to half an hour. You will be alone in the room during the scan; however, the technologist can see, hear and speak with you at all times. For pediatric patients, a parent may be allowed in the room with the patient to alleviate fear but will be required to wear a lead apron to prevent radiation exposure. When the exam is over the patient may be asked to wait until the images are examined to determine if more images are needed.

If your infant or toddler is having the test, the doctor may give your child a sedative to keep him or her calm and still. Your doctor will give you tips to help prepare your child.

Who interprets the results and how do I get them?
A radiologist, who is a physician experienced in CT and other radiology examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician. The personal physician's office will inform the patient on how to obtain their results.

What are the benefits and risks?

Benefits

• Unlike other imaging methods, CT scanning offers detailed views of many types of tissue including the lungs, bones, soft tissues and blood vessels.
• CT scanning is painless, noninvasive and accurate.
• CT examinations are fast and simple. For example, in trauma cases they can reveal internal injuries and bleeding quickly enough to help save lives.
• Diagnosis made with the assistance of CT may eliminate the need for invasive exploratory surgery and surgical biopsy.
• CT scanning can identify normal and abnormal structures, making it a useful tool to guide radiotherapy, needle biopsies and other minimally invasive procedures.

Risks

• CT does involve exposure to radiation in the form of x-rays, but the effective radiation dose from this procedure is about the same as the average person receives from background radiation in three years.
• Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant.
• Nursing mothers should wait 24 hours after contrast injection before resuming breast feeding.
• The risk of serious allergic reaction to iodine-containing contrast material is rare, and radiology departments are well equipped to deal with them. 

Some people report feeling a flush of heat and sometimes a metallic taste in the back of the mouth. These sensations usually disappear within a minute or two. Some people experience a mild itching sensation. If it persists or is accompanied by hives (small bumps on the skin), the itch can be treated easily with medication. In very rare cases, a patient may become short of breath or experience swelling in the throat or other parts of the body. These can be indications of a more serious reaction to the contrast material that should be treated promptly, so tell the technologist immediately if you experience these symptoms. Fortunately, these adverse effects are very rare.

Radiology Testing Instructions for CT Scan

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