This test, in most instances, has now been replaced by MRI and is only used when there is a contra indication to MRI - such as a pacemaker. Myelograms are special X-ray studies of the spinal canal, spinal cord and nerve roots. They are used to diagnose and evaluate conditions affecting the spinal canal, nerve elements (such as spinal stenosis and nerve root impingement) and prolapsed intervertebral discs. The test involves a special X-ray dye being placed into the spinal sac. Using a local anaesthetic, the radiologist injects the dye through a small needle inserted into the spine. This allows the radiologist to take a series of x-ray pictures on which the nerve roots are outlined. In this way, any abnormalities within the spinal canal can potentially be visualised to aid in diagnosis of certain spinal problems. The myelogram, with accompanying CT scan may take several hours, so it's advisable to have someone drive you home, rest for the remainder of the day and avoid strenuous activity. If you develop a headache following the test, drink plenty of fluids and lie flat on your bed.