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A Patient's Guide to CAT Scans

What it is: The CAT scan is an X-ray test that is similar to both the MRI and a regular X-ray, because it can show both bones and soft tissues. The CAT scan uses X-rays that are interpreted by a powerful computer to create images that appear as "slices" through the body. Today, using the computer software, these slices can be combined by the computer to actually give a 3-D view of the bones of the spine.

What the test shows: CAT scans are also able to produce X-ray "slices" taken of the spine, so each section of the spine can be examined separately. The CAT scan was developed before the MRI, and for several years, was used to show the soft tissues of the spine. The pictures of the soft tissues produced by a CAT scan are probably not as clear as the MRI. To make the soft tissues easier to see, the CAT scan is often combined with a myelogram. For the myelogram, dye is placed into the spinal sac to outline the nerves and spinal sac so they show up clearly on the X-ray. Because the CAT scan uses X-rays, it shows the bones of the body in great detail. It is the test of choice when looking at fractures or damaged bones due to infection or cancer.

What the test does not show: A CAT scan without dye is not as good at showing the discs and the nerves of the spine. The MRI is the best test to show problems such as a herniated disc. The CAT scan does not show muscles or ligaments clearly.

How the test is done: As with an MRI, a CAT scan will require you to lie on a table that slides into a scanner. The scanner is essentially an X-ray tube that rotates in a circle taking many pictures. The procedure takes 30-60 minutes. You will have to lie very still for short periods as the scanner is taking the pictures.

What risks the test has: The CAT scan uses X-rays (which use radiation). In large doses, this can increase the risks of cancer. The vast majority of patients who have a CAT scan will never get enough radiation to worry about cancer. Only patients who must have multiple X-rays and CAT scans (hundreds) over many years need worry about this risk. Children and young adults who plan to have children should be protected from radiation exposure to the testicles and ovaries. The radiation may damage the sperm and eggs. It is simple to protect the area whenever possible by shielding it with a lead apron or blanket.

What the test costs: A CAT scan of the spine usually has two costs associated with the test. The first cost is the fee for actually doing the test. This is called the "technical fee". The second cost is the fee of having a specialist, such as a radiologist, read and interpret the test. This is called the "professional fee". You may get two bills for this test: one from the hospital or clinic where you and the CAT scan done, and one from the specialist who read the test.

Copyright © 2003 DePuy Acromed.

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