An X-ray is a diagnostic test that images bones by shooting an X-ray beam through the body. The calcium in bones blocks penetration of the X-ray beam and the image of the bones is picked up as a shadow on a film positioned on the other side of the patient. X-rays provide for excellent bony detail because bone consists mainly of calcium. X-rays of the spine can be used to diagnose tumors, fractures, and spinal misalignment. However, discs and nerve roots do not have any calcium, so an X-ray does not capture an image of these structures. An X-ray cannot be used to diagnose lumbar disc herniation or other causes of nerve pinching.