What is it?

The CT or "CAT" scan is an X-ray test that shows bones and soft tissues. The abbreviation "CAT" stands for Computer Assisted Tomography. X-rays are taken and then interpreted by a powerful computer that makes them appear as "slices" through the body. Special software can combine these images into a three-dimensional view of the bones.

Why is it done?

The "slices" produced by a CT scan allow each section of the spine to be examined separately. The images show details of spine bones in great detail. A CT scan can show if bone spurs are pushing against spinal nerve roots. It is often used when looking at fractures or damaged bones due to infection or cancer. Some doctors have recently begun using CT scan technology on a limited basis to test for osteoporosis in the spine.

How is it done?

You will be asked to lie on a table that slides into a scanner. This is similar to having an MRI test. The scanner used for CT scans is essentially an X-ray tube that rotates in a circle. You will need to lie very still for short periods while the scanner takes many pictures. The procedure takes 30-60 minutes.

What are the limitations?

The CT scan does not show muscles or ligaments clearly. To make the nerves and soft tissues easier to see, this test is often combined with a myelogram. With the myelogram, dye is injected into the spinal sac to outline the nerves and spinal sac so they show up clearly on the CT scan. A CT scan without dye is not as good at showing the discs and the nerves of the spine. The CT scan was developed before magnetic resonance imaging (MRI). The pictures of soft tissues are not as clear as they are with an MRI. The MRI is a better test to show problems within the disc, particularly a recurring disc herniation. It is also helpful for showing the health of a disc following surgery.

What are the risks?

The CT scan uses X-rays. In large doses, radiation from the X-rays can increase the risk of cancer. The vast majority of patients who have a CT scan will never get enough radiation to worry about cancer. Only patients who must have large numbers of X-rays or CT scans-hundreds-over many years need to be concerned. Children, and young adults who plan to have children, should be protected from radiation exposure to the testicles and ovaries. Otherwise the radiation may damage the sperm and eggs. It is simple to protect these areas by shielding them with a lead apron or lead blanket.