Brief Summary:The purpose of this research study is to examine the effects of physical therapy on the spinal discs. Back pain is the number one cause of disability in the US, and the spine is the most common location of chronic pain in Veterans. Physical therapy is often very effective at improving patients’ back pain, but it does not work for everyone, and it is not understood how physical therapy alters the tissues within the spine. With this research the investigators hope to learn if the investigative team can measure changes to the spinal discs on MRI scans that might predict if a patient’s back pain will improve with physical therapy or not.