Web Hosting by Netfirms | Free Domain Names by Netfirms

CAT Scan Procedure

CAT is an acronym for "computerized axial tomography." CAT has been replaced with a new acronym, CT, that simply stands for "computed tomography." Tomography is the process of making an image of a plane through the body. A CAT scan or a CT scan is a procedure that uses x rays, radiation detectors, and computers to produce images of planes through the body. Rather than using conventional x-ray film to intercept and record information in the x-ray beam that passes through the body, CT scanners use radiation detectors. The x-ray tube and the radiation detectors are positioned on opposite sides of the body. The x-ray tube and detectors rotate around the body. As this is happening, the detectors accumulate information about how much of the x-ray beam passes through the body. This information from the detectors is fed into a computer that performs millions of calculations and determines what must have been in the path of the x-ray beam to absorb x rays the way they were absorbed as they passed through the body. The computer then creates an image that represents a slice (plane) through the body traversed by the x-ray beam. Conventional x-ray procedures give images such as you would see in looking at a hard-boiled egg from the side. CT scans let the radiologists see planes through the egg such as you would see if you put the egg through an egg slicer and then removed each slice and looked down on the top of the egg. As you peel off each slice, you begin to see the yolk getting larger with each slice. Once you pass the middle of the yolk, it begins to get smaller with each slice removed. By creating a series of CT images (slices) down the body, the radiologist can look at each image and get an accurate indication of position, size, and density of objects within the body. Some newer computers can take all of the slices (images of planes through the body) and assemble them into a 3-D image that can be rotated and looked at from various directions. CT scanners are very important diagnostic tools in modern radiology.[Miller]

CT scans are performed to evaluate: · abnormalities that showed up on other other types of x-rays. · injuries. · tumors related to cancer. CT scans can indicate the progress of some cancers if the cancers spread or metastasize and the effectivness of treatment. · bony abnormalities. · brain abnormalities. · abdominal symptoms. Use of CT scans in these cases can often prevent exploratory surgery. · suspicious chest abnormalities.

CT scans are also used to guide needles when taking tissue samples. In addition, the technique is useful in gauging a person's recovery after an operation. CT scans can also be used to guide instruments for surgery deep in the brain.

How is the test performed?

A person having a CT scan will need to undress and put on an exam gown. Next, the person will lie on a narrow table. The table will slide through a machine that looks like a doughnut. This is called the gantry. While in the gantry, an x-ray tube travels around the individual creating computer-generated x-ray images.

Some types of exams require the individual to receive an intravenous injection of iodinated contrast, which is a dye that makes some tissues show up better. Scans of the intestines sometimes call for the person to drink diluted iodinated contrast solution prior to the exam. After the exam, the technologist will view the pictures. If they are adequate, the person is free to leave.

What is involved in preparation for the test?

A person having the test will be asked to refrain from eating or drinking for 4 hours before the scan. All jewelry and metal objects that may interfere with the exam need to be removed beforehand, as well. Women will be asked if they are pregnant. Individuals should check with their healthcare provider or hospital x-ray department to see if any other preparation is needed.

What do the test results mean?

A CT scan provides a direct image of soft tissue structures such as the, liver, lung, spleen, pancreas, lymph nodes and fatty tissues. CT is also good for identifying and tracking large abnormalities such as tumors. CT of the head can be used to evaluate strokes, tumors, bleeding and injuries. It can also be used to examine most brain structures. CT performs well in providing images of bony structures. These include the spine, facial bones, sinuses and skull. It also works well in viewing long bones for fractures, tumors or infection. [Discovery Health]

Sources
Ken Miller, CHP, Medical Health Physics
Discovery Health on-line, http://discoveryhealth.com; 9/04/2002