Your doctor may order a computed tomography examination to aid in the diagnosis and treatment of your foot and ankle problem. Computed Tomography (CT) imaging, also known as "CAT scanning" (Computed Axial Tomography), combines the use of a digital computer together with a rotating x-ray device to create detailed cross sectional images or ""slices"" of the different parts, particularly bony structures, of the foot and ankle. This test helps to delineate the structures of your foot and ankle and can give your doctor 3-D visualization of these structures to aid in your treatment. For many patients, CT can be performed on an outpatient basis without requiring admittance to a hospital. CT imaging is commonly ordered for the following foot pathologies:
- Bone Tumors
- Fractures - acute and stress fractures
- Non-unions or delayed unions
- Foreign Bodies
- Degenerative and rheumatoid arthritis
- Angular deformities
- Flat feet
- Cavus feet
- Post-operative monitoring
- Avascular necrosis
During the procedure, you will lie very still on a table. This table passes your foot and ankle through the x-ray machine, which is shaped like a doughnut with a large hole. The machine, which is linked to a computer, rotates around the patient, taking pictures of one thin slice of tissue after another. The length of the procedure depends on the size of the area to be x-rayed. The computer then processes images from these x-rays. The final image, called a "computed tomogram" or "CT slice," is displayed on a cathode-ray tube (CRT), a device similar to a television picture tube and screen. This image can be recorded permanently on film or can be stored on magnetic tape or optical disk.
Computed tomography offers some advantages over other x-ray techniques in diagnosing disease, particularly because it clearly shows the shape and exact location of soft tissues and bones in any "slice" of the foot and ankle. CT scans help doctors distinguish between a simple cyst and a solid tumor and any involvement of the bone. CT scanning is more accurate than conventional x-ray in determining the stage (extent) of some bone tumors. Information about the stage of the disease helps the doctor decide how to treat it.
Spiral CT scanners are one of the latest innovations. They use continuous scanning to generate cross-sectional slices and make a set of 3-dimensional images. Spiral CT has decreased the time it takes to produce tomographic pictures.
In preparing for the examination, you can eat and take your normal medications. The examination will take from 45 minutes to an hour based on the area being scanned. Patients are encouraged to bring something to read or do in case there are any delays prior to their CT exam. Patients should wear comfortable, loose fitting clothing for their CT exam. Some people may be concerned about the amount of radiation they receive during a CT scan. It is true that the radiation exposure from a CT scan is slightly higher than from a regular x-ray. Because of the radiation exposure, pregnant women should not have a CT exam or any x-ray examination, especially if the woman is in her first trimester (first of three-3 month periods of pregnancy). Depending on the condition, there may be other exams available, such as ultrasound, to help diagnose a medical condition. Pregnant women should always inform their imaging technologist or radiologist that they are pregnant, or may be pregnant.
Your physician will discuss the results with you. If you have any further questions regarding why this test was ordered for you, please ask your physician.