A myelogram is an X-ray study that involves the injection of a dye into the spinal canal to assess the nerve roots. A needle is injected into the thecal sac containing the nerve roots with radiopaque dye that will highlight the nerve areas in the X-ray image.

A myelogram is typically used to evaluate for disk pathology and degenerative changes of the spine. Although the technique has been largely replaced by the MRI, a CT scan with a myelogram may be used since it is more sensitive and can diagnose even subtle cases of nerve root pinching.