A patient history entails reviewing when the pain occurs, where it is located, how it began, the previous treatment and the extent to which it limits the patient's activities. Additionally, the physician will try to determine if other factors (such as depression) may be contributing to the patient's back pain. An individual's general health will also be reviewed as it can influence the role of spine surgery (e.g. heart or lung disease). A physical examination is done to determine whether there is evidence for any neurologic (nerve-related) injury. There are a number of diagnostic studies that are available to investigate the etiology (medical cause) of the pain. The most common study is an X-ray of the low back, which can show if there is some boney instability or deformity to the spine. It can also image such things as a fracture, or in advanced stages, it can show tumors of the spine. Although done frequently, they usually fail to demonstrate the cause of the back pain. The gold standard is to follow X-rays with magnetic resonance imaging (an MRI scan). MRI scans provide very precise anatomic information about the health of the discs as well as presence of any tumors or compression on the nerves. A discogram, which is a more controversial study, may also be performed before spine fusion surgery. This study involves inserting a needle into the disc and injecting dye. If this process causes the patient's normal pain to occur, it is presumed that the specific disc is the anatomic cause for the pain.