What is a computed tomography (CT) scan?

A CT scan is a kind of X-ray that makes pictures of internal organs, bones, disks and blood vessels. Images are stored on a computer and can produce a series of detailed images or "slices" of the part of the body studied. Each slice takes a few seconds to record. CT scans may be done for any part of the body, including the brain.

Why is a CT scan ordered for me?

Your physician uses the CT scan of the neck, thoracic spine or lumbar spine to detect spine problems such as herniated disks, osteoporosis, injuries, tumors, deformities and problems with the spinal cord. It can be used to show internal organs, such as the liver, kidneys, heart, lungs and pancreas. It is good at showing bones and for looking for fractures.

A CT of the head may be ordered to obtain information about tumors, bleeding in the head, aneurysms, blood clots, infection and stroke. CT also can show problems with eyes and optic nerves, inner-ear bones and nerves leading from the ear to the brain, and the sinus cavities.

A CT scan often shows bony structures better than magnetic resonance imaging.

What happens during the CT scan?

You will be asked to remove all jewelry. You will lie on a hard table that will slide into a cylindrical opening in a large machine called a scanner, which contains the X-ray tube. While the table slides into the scanner a small distance at a time, the cylindrical part revolves around you. As this happens, you may hear clicking. Each time the table stops, a new slice picture is taken.

You will be alone in the scanning room, but you can talk with the X-ray technologist, who can see you. Any movement you make will cause the image to be blurred. You must lie completely still.

How is a CT with contrast done?

Your physician may order the CT with contrast before surgery to pinpoint nerve or spinal-cord pinches and to see blood vessels and organs better. If you have had a previous spine fusion, sometimes contrast may be ordered to help determine the status of the fusion. Contrast is a dye that contains iodine. Depending on the part of the body to be studied, contrast is injected through an intravenous line, taken by mouth or injected into the thin, saclike covering of the spinal cord. A CT scan may be done before and after the contrast is given.

When contrast is injected into the intrathecal sac, it is called a myelogram. When less dye is used, it may be called a low-dose CT. If you are having the CT with intrathecal contrast, the radiologist will usually give you Valium pills for relaxation. Sometimes Valium is given intravenously.

You will lie on your side on the X-ray table so your physician can best see your lower back using X-ray guidance. The skin on your back will be scrubbed using two types of sterile soap. The physician will numb a small area of skin on your lower back with numbing medicine. This medicine stings for several seconds. After the numbing medicine has been given time to be effective, your physician will insert a small needle using X-ray guidance into the intrathecal sac. Contrast is injected, and you will be moved to a position that allows the contrast to reach the area to be imaged. You will then be transferred to the scanner where pictures will be taken of the area to be studied.

How long does the CT scan usually take?

The scan may take from 20 to 60 minutes, depending on the areas to be scanned.

What will I need to do before and after the CT?

There are no special instructions before or after a normal CT. Wear loose, comfortable clothing and arrive at the hospital at the appointed time. You can drive and resume your activities afterward. But if you are claustrophobic and require sedation to go into the scanner, you will need someone to drive you home. Please tell the person who schedules your appointment if being enclosed in small spaces is a problem.

If you are having a CT with contrast, there are some special instructions:

• Bring your routine and pain medicines with you. Do not take any other medicines after you arrive at the hospital without permission from the nurse.
• Do not eat anything after midnight the night before the test. If you take daily medicine, take it with a sip of water and be sure to tell the nurse or technician what you have taken and when.
• Drink extra fluids the day before the test, especially caffeinated drinks. This will help increase fluid in your body and decrease your risk of developing a spinal headache.
• If you are an insulin-dependent diabetic, do not change your eating pattern before the procedure.
• If you are on blood thinners or a diabetic medicine, tell you physician so the timing of these medicines can be explained.
• Leave valuables at home.
• Take your routine medicines, such as high blood pressure and diabetic medicines.
• You will be at the hospital four or five hours for your procedure.
• You will need to bring a driver with you. You may return to your activities, including work, two days after the procedure.