If you have persistent or serious back pain, and especially if you are a candidate for surgery, your doctor may order one or more imaging studies to pinpoint or confirm the cause of back pain. These studies, each of which has benefits and limitations, provide a view of the bones and the soft tissues (muscles, ligaments, cartilage, tendons, and blood vessels).
Diagnosing the Cause of Back Pain with X-rays.
X-rays should be the first imaging study for chronic back pain and for new-onset back pain lasting longer than four to six weeks. They are especially useful for detecting fractures and invasion of bone by multiple myeloma.
X-rays are generally overused, but they may be needed for people over age 50 because these individuals have a greater risk of malignancy and vertebral fractures. People should not be concerned about the possible risks of modern x-rays; the radiation doses are low and there is no evidence of harm even from repeated x-rays. Conventional x-rays are available almost anywhere and are relatively low in cost.
Diagnosing the Cause of Back Pain with Computed Tomography (CT) scans.
A CT scan, also called a computerized axial tomography (CAT) scan, involves a series of x-rays that are taken as a special detector rotates 360° around the patient. A computer combines all the information into a cross-sectional picture. CT scans are 10 to 20 times more sensitive than x-rays; they provide better soft-tissue detail and good detail of the vertebrae.
Although MRI scans or CT myelograms (see below) are even more useful for examining the soft tissues (for example, herniated disks), CT scans are still best for studying bone problems—for example, bone destruction due to infection. CT scans are considerably more expensive and deliver more radiation than conventional x-rays.
Diagnosing the Cause of Back Pain with CT myelogram.
A CT myelogram involves a CT scan after the injection of a contrast material into the spinal canal. The injection carries the risk of infection and such side effects as nausea, headaches, and pain or discomfort at the site of injection, and people are required to sit or lie with their head elevated for six to eight hours afterward. These scans offer the best detail of bone and soft tissue. CT myelograms are usually performed only prior to surgery or after failed surgery.
Diagnosing the Cause of Back Pain with Magnetic resonance imaging (MRI).
In MRI, the most sensitive imaging technique, the patient is surrounded with a powerful magnet while radio waves are passed through the body. No x-rays are involved. This test provides the best images of soft tissues and is completely safe. However, MRI may not give a useful image of the bones in the spine. MRI is not recommended for early diagnosis of back pain unless the doctor suspects a serious condition, such as cauda equina syndrome.
Despite their sensitivity, studies have shown that MRIs should be reserved for preoperative evaluation or for people with a suspected herniated disk whose back pain symptoms do not respond to conservative treatment after four to six weeks.
MRI commonly visualizes disk abnormalities. In one study, at least one disk was affected in 64% of people who had no back pain. Disk herniation was present in 27% of these subjects (this number increased with age). Thus, the abnormalities revealed by an MRI are not necessarily the cause of a person’s back pain. In addition, this technique is costly, and MRI devices are not available everywhere.
Because people must lie perfectly still for between 30 minutes and two hours in a relatively small space, MRIs may be uncomfortable and poorly tolerated by those who are claustrophobic. (Open MRIs produce less claustrophobia but generally do not provide high-quality views and are not recommended.) In addition, depending on which part of the spine requires the MRI, it usually cannot be used in people with intrauterine devices, metal joint replacements, aneurysm clips, implantable cardioverter-defibrillators, or pacemakers.
Diagnosing the Cause of Back Pain with Bone Scans.
Bone scans measure the amount of radioactivity emitted from bone after the injection of a bone-seeking compound that contains technetium, a radioactive metal. The bone is scanned two to three hours after the injection, and information about the distribution of the radioactive compound in the bone is fed to a computer, which produces a two-dimensional image of the bone.
An area of bone that displays an increased uptake of technetium has a higher rate of bone turnover, which can be the result of a fracture not identified on an x-ray as well as metastatic cancer, Paget’s disease, or osteomyelitis (a bacterial infection of the spine). The amount of radiation delivered is similar to that of a CT scan. This technique can be used to identify fractures in both the central and peripheral areas of the body.
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