Keywords:
X-ray, Fluoroscopy, MR, MRI, CT, Arthrogram, Bone Scan
Imaging studies are special studies that your doctor may order to help diagnose your injury or condition. Here is a list of commonly used imaging studies.
X-rays are the most common study used in Orthopaedic Surgery. Different tissues in the body, especially bone, will block the x-rays from passing through the body onto a sheet of film. Thus x-rays are an excellent way to visualize the bones in the body. This is useful for diagnosing fractures, dislocation, arthritis, tumors, growth injuries, and many other conditions. While X-rays are a form of radiation, they are generally extremely safe to the body in doses and quantities typically obtained by your doctor.
Fluoroscopy is a form of x-ray. It is like an x-ray movie, where the body’s bones can be visualized in real time. It is very valuable when looking for abnormalities that show up only during activity or motion, or when a joint is stressed. Flouroscans use extremely low doses of radiation, and are quite safe.
MR scans (MRI, Magnetic Resonance Imaging) are a valuable way to visualize the soft tissues in the body, such as tendons, ligaments, muscles, and other organs. The MR scan uses a magnetic field, not radiation. Basically, you lie still on a flat table, with the MR tube over the body part, in a magnetic field. A computer is able to analyze the data (how fast hydrogen atoms change their spin direction!) and provide exquisitely detailed pictures of slices of your body. It is painless and safe, but people with significant claustrophobia may require some sedation. It is not cheap: about a thousand dollars per scan. It is also not perfect, and one must be careful not to rely too heavily on the MR scan. It does a poor job with bones and cartilage.
CT scans (CAT scans, Computed Axial Tomography) are another form of specialized x-rays. They look a lot like a MR scan, and you also have to lie still on a table with the CT scanner over you. The CT scan will also provide detailed pictures of slices of your body, but it works best on bones, and works relatively poorly for soft tissues. The CT scan is useful to look for fractures or other bony injuries, when the plain x-ray is difficult to interpret.
Arthrogram An arthrogram is a study where a special dye is injected into a joint. This dye shows up on x-ray, and an x-ray of the joint while the dye is being injected can reveal information about soft tissues such as muscles and ligaments, even if they aren’t seen directly. Typically, an arthrogram is positive when dye is seen traveling into an area it shouldn’t normally go to, implying a tear of another structure. Arthrograms have generally been replaced by MR. Although they are a lot cheaper that MR scans they are invasive and fairly uncomfortable. There are other limitations with Arthrograms: just because the dye doesn’t cross into an area, doesn’t mean its not torn anyway. Think of the one-way valve on an inflatable pool toy.
Bone Scan A bone scan is a study that looks at relative blood flow to parts of the body. A small amount of a patient’s blood is withdrawn, and a short acting radioactive isotope is attached to the red blood cells. The ‘radioactive’ blood is then reinjected back into the body. The patient lays on a table, which is really a big geiger counter. Wherever the blood flows in the body will show up on the scan. It just so happens that the skeleton has a tremendous amount of blood flow through it, compared to the rest of the body. Therefore, a bone scan will provide a picture of blood flow through the skeleton. Certain conditions cause a relative increase in local blood flow, such as a fracture, infection, or tumor. A bone scan is very sensitive at detecting this. By the way, the radioactive isotope is very weak, short-acting, and not very dangerous. It is expensive, however.
The most important reason for ordering any test or study is only if the results of that test will aid in making a diagnosis, or change the decisions regarding treatment. One should not order a test simply for the sake of ordering it. Many of these tests are expensive, and uncomfortable. Care should be taken regarding the relative risk and benefit before any study is ordered.