When a physician is evaluating a person with joint pain and swelling, he or she may use x-rays to determine whether the arthritis has caused damage to the bones of the joint. Radiographs, as x-rays are sometimes called, are especially important if the doctor suspects RA. He or she will often order that x-rays be taken of any swollen joints. Although x-rays cannot confirm the presence of RA, they can be a useful tool for distinguishing between RA, osteoarthritis, and other conditions. Additionally, x-rays establish a baseline for comparison. As the disease progresses, they can be used to monitor changes in the bones over time. Early in the course of the disease, the bone changes associated with RA do not always appear on x-rays because bone damage is not yet visible. In general, xrays are more useful later in the disease, when bones may be affected more dramatically.
Early in the course of the disease, the bone changes associated with RA do not always appear on x-rays. In general, x-rays are more useful later in the disease, when bones may be affected more dramatically.
Often, as part of a person's initial evaluation with a rheumatologist, chest x-rays are ordered in addition to x-rays of any swollen joints. Chest x-rays are performed to evaluate the lung for diseases that are sometimes associated with arthritis (see Question 18).
X-rays are usually performed in a special hospital department (Radiology) by a radiologic technician or a radiographer, who will tell you which part of your body is to be imaged. These technicians are highly skilled. They must have college degrees, receive additional training in their field, and pass a state licensing examination before they can take x-rays. The training for a radiologic technician is different from that of a radiologist; the latter professional is a physician who is trained to interpret x-ray images.
To make the image, x-rays are passed through your body and captured on special film. This x-ray film is then developed and examined. Standard x-rays are particularly good at showing abnormalities of the bone. Unfortunately, because they rarely show problems in soft tissues, x-rays cannot show early signs of arthritis very well. Despite this drawback, examination of x-rays can help the doctor to diagnose arthritis by highlighting damaged areas on the bone.
The way bones appear on x-rays can vary in normal people and changes occur with age. For example, age-related abnormalities are frequently seen on x-rays of the spine, even in people without pain. Many people may have normal-looking x-rays despite suffering severe pain from inflammation in or around the joints. In addition, x-rays can show apparent damage or abnormalities that may not be the cause of the pain, swelling, or stiffness. For these reasons, your doctor will not rely on x-rays alone to make the diagnosis of RA, but will interpret the images alongside findings from the physical examination or other tests.
Other Imaging Methods
In addition to the standard x-ray of the joint or bone, other ways of imaging the body are used to identify signs of RA.
In arthrography, dye is injected into the joint to allow it to show up in more detail when x-rayed. Occasionally, dye may be injected into a blood vessel to assess the circulation under x-ray (this is called an arteriogram or venogram).
Computerized tomography (CT) uses x-rays that record images of sections or “slices” of the body. These multiple images are then processed by a computer to produce cross-sectional pictures of the body part. CT scans can give detailed pictures of the skeleton, but will also show other types of tissue, such as the muscles, which cannot be seen on an ordinary x-ray.
An isotope is a chemical that gives off a type of radioactivity called gamma rays. In an isotope bone scan, a very small amount of the isotope is injected into the blood and is taken up by the bones. The gamma rays are then detected by a special camera, and this information is sent to a computer, which combines the data to build a picture showing which areas of the bone are inflamed. The dose of radiation delivered with this imaging technique is very small and will quickly be excreted from the body in the urine.
Magnetic resonance imaging (MRI) uses high-frequency radio waves in a strong magnetic field to produce highly detailed pictures of the body. The radio waves interact with the water molecules in the body's tissues, and the signals that come back are processed by a computer to build up pictures of the inside of the body. An MRI scan produces pictures of the soft tissues—particularly cartilage, tendons, and nerves—that cannot be detected by x-rays. This technique is often used to detect early or minor abnormalities in these soft tissues; it can also detect signs of inflammation. MRI scans are particularly useful for the spine, the shoulder, and the knee. They can show numerous differences between individuals, many of which are completely normal, so it is important that the results be interpreted by the doctor who has ordered the imaging investigation.
Magnetic resonance imaging (MRI)
A diagnostic technique in which radio waves generated in a strong magnetic field are used to provide information about the hydrogen atoms in different tissues within the body. A computer then uses this information to produce images of the tissues in many different planes.