Discography is a radiographic technique to identify painful intervertebral discs. With the use of an x-ray machine, a thin needle is advanced into an intervertebral disc. First, dye is injected into the disc to visualize the integrity of the center and outer portions of the disc. If pain is generated, an anesthetic is injected to resolve pain. This is considered a positive test. The test is used to determine the source of back pain when other radiographic techniques have been inconclusive in finding a source of pain. The procedure is often damaging to spine structures and may not be predictive of the benefit of spinal surgery for abnormal disc levels.