The purpose of this procedure is to demonstrate abnormalities of the nerves or any compression on the dural sack, which carries the nerve routes from the brain to the rest of the body through the spinal canal. For example a herniated disk. Nowadays this study is reserved for patients who cannot undergo a magnetic resonance (MRI) study to investigate their symptoms. When it is performed it is often combined with a CT study of the region of interest (e.g. lumbar spine).