Imaging tests can allow your doctor to see the internal structures of your back non-invasively. It's important to note, however, that just because an imaging test shows a structural abnormality, it isn't necessarily the source of pain. For example, a large percentage of older people have changes due to osteoarthritis, disc bulges and even herniated discs that can be seen by X-ray, yet only a small percentage of those people have back pain.

The most common imaging tests to diagnose back problems are:

X-ray (radiography). A standard X-ray is a simple test in which an X-ray beam (a form of electromagnetic radiation) is passed through the hip to create a two-dimensional picture of the bones. Your doctor can use X-rays to view:
• changes of the spine due to osteoarthritis
• problems with the spine alignment
• a vertebral fracture
• bony changes characteristic of ankylosing and other spondylarthropathies.

Because X-rays only show the bones, your doctor will order different imaging tests if he wants to see the soft tissues of the back, including:

Learn more about x-rays of the thoracic spine and lumbar spine from MedlinePlus. 

Computerized axial tomography (CAT) scan. Also called a computed tomography (or CT) scan, this is noninvasive test combines X-ray equipment with sophisticated computers to record two-dimensional slice images of your body and, in some cases, turning those slices into a three-dimensional view of the back. CT scan shows soft tissues such as ligaments and muscles more clearly than traditional X-rays do, so it is more useful for diagnosing certain problems, such as ruptured or degenerated discs, spinal stenosis, tumors or infections of the spinal cord.

Magnetic resonance imaging (MRI).  This procedure uses a strong magnet linked to a computer to create a detailed image of a cross section of the body in black and white and shades of gray. The advantage of MRI scans over X-rays and CT scans is that MRI provides clear, detailed images of the soft-tissue structures, such as the muscles, cartilage, ligaments, discs, tendons and blood vessels, in addition to the bones.

Learn how new MRI technology may enable early osteoarthritis diagnosis

Bone scan. In bone scan, a small amount of radioactive dye is injected into a vein in your arm and allowed to circulate through your body, including the bones of your spine, for a couple of hours. A special camera is then used to scan the area in question and produce a picture. The scan works by detecting any area of the spine that has an increase in blood flow and bone-forming cell activity, which could possibly indicate a tumor, infection or fracture.

Discogram. A discogram is a test used to view and assess the internal structure of a disc and to determine if the disc is a source of pain. To perform a discogram, a doctor injects a radiopaque dye (a dye that shows up on radiological scans) into the disc or discs being examined. The doctor then performs a CT scan, in which any tears, scars or changes in the disc are illuminated.

Dual energy X-ray absorptiometry (DEXA or DXA). DEXA is used to diagnose osteoporosis. The test uses a small amount of radiation to determine the density, or thickness, of bone in the spine and other areas of the body. Although DEXA is the most commonly used test for bone density, there are others.