Computed Tomography

Computed tomography is a diagnostic procedure in which cross-sectional pictures or "tomographic slices" of the body are made by x-ray. This technique may also be called a CT scan or CAT scan.

During the procedure, the animal lies on a table. The table passes 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. To obtain a clearer picture, the animal may be injected with a contrast material. The length of the procedure depends on the size of the area to be x-rayed.

Images from these x-rays are then processed by the computer. 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. In addition, a CT scan 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 organs, soft tissues, and bones in any "slice" of the body. CT scans help doctors distinguish between a simple cyst and a solid tumor and, thus, evaluate abnormalities more accurately. CT scanning is more accurate than
conventional x-ray in determining the stage (extent) of some types of cancer. Information about the stage of the disease helps the doctor decide how to treat it. CT scanning is also used to plan radiation therapy or surgery. The scans help doctors target treatment to the cancer and protect healthy tissue.

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.