A computed tomography (CT) scan of the lumbar spine is an imaging method that uses x-rays to create cross-sectional pictures of the lower back (lumbar spine).

CT rapidly creates detailed pictures of the lower back. The test may be used to evaluate:

• Birth defects of the spine in children
• The lower spine after severe trauma
• Other spine problems when MRI cannot be used

Lumbar CT scan can also be used during or after an x-ray of the spinal cord and spinal nerve roots (myelography) or an x-ray of the disk (discography).

You will be asked to lie on a narrow table that slides into the center of the CT scanner. You will lie on your back with your arms up over your head.

Once you are inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam in one continuous motion.)

Small detectors inside the scanner measure the amount of x-rays that make it through the lower back. A computer takes this information and uses it to create several individual images, called slices. These images can be stored, viewed on a monitor, or printed on film. Three-dimensional models of the lumbar spine can be created by stacking the individual slices together.

You must be still during the exam, because movement causes blurred images. You may be told to hold your breath for short periods of time.

The exam should take 15 - 30 minutes.

Certain exams require a special dye, called contrast, to be delivered into the body before the test starts. Contrast can highlight specific areas inside the body, which creates a clearer image.

Some people have allergies to IV contrast and may need to take medications before their test in order to safely receive this substance.

Contrast can be given in several ways.

• It may be delivered through a vein (IV) in your hand or forearm.
• It may be given as an injection into the space surrounding the spinal cord.

If contrast is used, you may also be asked not to eat or drink anything for 4-6 hours before the test.

If you weigh more than 300 pounds, have your doctor contact the scanner operator before the exam. CT scanners have a weight limit. Too much weight can cause damage to the scanner's working parts.

Since x-rays have difficulty passing through metal, you will be asked to remove jewelry and wear a hospital gown during the study.

Some people may have discomfort from lying on the hard table.

Contrast given through an IV may cause a slight burning sensation, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.