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Computed tomography (CT) scan, also called computerized axial tomography (CAT) scan, is used to create cross-sectional images of structures in the body. In this procedure, x-rays are taken from many different angles and processed through a computer to produce a three-dimensional (3-D) image called a tomogram.
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CT scans are pictures taken by a specialized x-ray machine. The machine circles your body and scans an area from every angle within that circle. The machine measures how much the x-ray beams change as they pass through your body. It then relays that information to a computer, which generates a collection of black-and-white pictures, each showing a slightly different “slice” or cross-section of your internal organs. Because these “slices” are spaced only about a quarter-inch apart, they give a very good representation of your internal organs and other structures. Doctors use CT scans to evaluate all major parts of the body, including the abdomen, back, chest, and head.
A CT scan is not a very common test to have done for back problems. It does a better job showing the abdominal internal organs than showing details of the bones in the spine. But some back pain is caused by problems in these internal organs, such as the pancreas or the kidney. The CT scan is an excellent way to examine these organs. Also, the CT scan can be combined with a test called a “myelogram” (discussed separately) to give a clear view of the spinal cord and places where the vertebral bones might be pinching it.
Why It Is Done
A CT scan of the spine is done to:
*Look at the bones of the spine (vertebrae).
*Find problems of the spine, such as tumors, fractures, deformities, infection, or narrowing of the spinal canal (spinal stenosis).
*Find a herniated disc of the spine.
*Check to see if osteoporosis has caused compression fractures.
*Check on problems of the spine that have been present since birth (congenital).
*Look at problems seen during a standard X-ray test.
*Check how well spinal surgery or therapy is working for a spine problem.
How do you prepare for the test?
If you are having an abdominal CT scan, you might have to fast 2–4 hours before your test. You also may have to drink a large quantity of oral contrast, a fluid that will show up on the CT scan and help define the lining of some internal organs. Tell your doctor if you’re allergic to x-ray contrast dyes, may be pregnant, or have diabetes and take insulin. Insulin can cause hypoglycemia after missing a meal.
What happens when the test is performed?
The test is done in the radiology department of a hospital or in a diagnostic clinic. You wear a hospital gown and lie on your back on a table that can slide back and forth through the donut-shaped CT machine.
During the test, you will lie on a table that is attached to the CT scanner, which is a large doughnut-shaped machine. The CT scanner sends X-rays through the body. Each rotation of the scanner takes a second and provides a picture of a thin slice of the organ or area being studied. One part of the scanning machine can tilt to follow the curve of your spine. All of the pictures are saved as a group on a computer. They also can be printed.
In some cases, a dye (contrast material) may be put in a vein (IV) in your arm or into the spinal canal (intrathecally). The dye make structures and organs easier to see on the CT pictures. The dye may be used to check blood flow and to look for tumors, areas of inflammation, or nerve damage.
The technologist moves the table with a remote control to enable the CT machine to scan your body from all of the desired angles. You will be asked to hold your breath for a few seconds each time a new level is scanned. The technologist usually works the controls from an adjoining room, watching through a window and sometimes speaking to you through a microphone. A CT scan takes about 30–45 minutes. Although it’s not painful, you might find it uncomfortable if you don’t like to lie still for extended periods.
How It Feels
You will not have pain during the scan. The table you lie on may feel hard and the room may be cool. It may be hard to lie still during the test.
Some people feel nervous inside the CT scanner.
If a medicine to help you relax (sedative) or a dye (contrast material) is used, an IV is usually put in your hand or arm. You may feel a quick sting or pinch when the IV is started. The dye may make you feel warm and flushed and give you a metallic taste in your mouth. Some people feel sick to their stomach or get a headache. Tell the technologist or your doctor how you are feeling.
The chance of a CT scan causing a problem is small. The contrast dye used in the test can damage your kidneys, especially if they are already impaired by disease.However, some newer dyes are less likely to cause kidney injuries. If kidney damage does occur, this is usually temporary, although in some rare cases it becomes permanent. If you are allergic to the dye used in the procedure, you may get a rash or your blood pressure may drop enough to make you feel faint until you get treatment. As with x-rays, there is a small exposure to radiation. The amount of radiation from a CT scan is greater than that from regular x-rays, but it’s still too small to be likely to cause harm unless you’re pregnant.
If you have diabetes or take metformin (Glucophage), the dye may cause problems. Your doctor will tell you when to stop taking metformin and when to start taking it again after the test so you will not have problems.You may have nausea or vomiting after the test.
There is a small chance of an infection at the needle site on your spine or bleeding into the space around the spinal cord.Intrathecal injections may cause a headache. On rare occasions, seizures may occur after an injection of intrathecal contrast material.
There is a slight chance of developing cancer from having tests that use radiation. The chance is higher in children or people who have many radiation tests. If you are concerned about this risk, talk to your doctor about the amount of radiation this test may give you or your child and confirm the test is needed.
Must you do anything special after the test is over?
A computed tomography (CT) scan uses X-rays to make detailed pictures of the spine and vertebrae in the neck (cervical spine), upper back (thoracic spine), or lower back (lumbosacral spine).
The radiologist may discuss the CT scan with you right after the test. However, complete results usually are ready for your doctor in 1 to 2 days.
If you face any problem After the test is over
Call 911 or other emergency services immediately if you have a seizure.
Call your doctor immediately if you:
*Have pain, weakness, or numbness in your legs.
*Have a severe headache.
*Have a headache that lasts more than 24 hours.
*Feel extremely irritable.
*Have problems urinating or having a bowel movement.
*Develop a fever.
What Affects the Test
The following may stop you from having the test or may change the test results:
*Pregnancy. CT scans are not usually done during pregnancy.
*Barium and bismuth used for another test. These substances show up on a CT scan. If a CT scan of the lower back is needed, it should be done before any tests that use barium, such as a barium enema.
*Metal objects in the body. These items, such as surgical clips or metal in joint replacements, may prevent a clear view of the body area.
*You are not able to lie still during the test.
What To Think About
*Sometimes your CT test results may be different than those from other types of X-ray tests, magnetic resonance imaging (MRI), or ultrasound scans because the CT scan provides a different view.
*CT results are often compared to positron emission tomography (PET) results to help find cancer. Some new scanners do both scans at the same time.
*MRI may give more information than a CT scan about the spinal discs and spinal cord. For more information, see the medical test Magnetic Resonance Imaging (MRI).
*When a CT scan of the spine is done with a myelogram, it is called a CT myelogram. An MRI of the spine is often done in place of a CT myelogram. For more information, see the medical test Myelogram.