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Computed Tomography (CT or CAT Scan)

What is a CT or CAT scan?

A CT or CAT scan is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce images (often called slices) of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, organs, and blood vessels. CT scans are more detailed than standard X-rays.

In computed tomography, the X-ray beam moves in a circle around the body. This allows many different views of the same organ or structure, and provides much greater detail. The X-ray information is sent to a computer and displays the structure imaged in a 2-D or 3-D form.

CT scans may be done with or without contrast. "Contrast" refers to a substance taken by mouth or injected into an intravenous (IV) line that causes the particular organ or tissue under study to be seen more clearly. Contrast examinations may require you to fast for a certain period of time before the procedure.

CT scans may be performed for various reasons but can help diagnose tumors, investigate internal bleeding, check for internal injury, evaluate blood vessels and generally evaluate many structures of the body.

Advances in computed tomography technology include the following:

  • High-resolution computed tomography. This type of CT scan uses very thin slices which are effective in providing greater detail in certain conditions such as lung disease.
  • Helical or spiral computed tomography. During this type of CT scan, both the patient and the X-ray beam move continuously. The images are obtained much more quickly than with standard CT scans. The resulting images have greater resolution and contrast, thus providing more detailed information. Multi-detector row helical CT scanners may also be used to obtain information detailed high resolution images in a short period of time.
  • Computed tomographic angiography (CTA). Angiography is an X-ray image of the blood vessels. A CT angiogram uses CT technology rather than standard X-rays or fluoroscopy to obtain images of blood vessels such as the coronary arteries of the heart.
  • Combined computed tomography and positron emission tomography (PET/CT). The combination of computed tomography and positron emission tomography technologies into a single machine is referred to as PET/CT. PET/CT combines the ability of CT to provide detailed anatomy with the ability of PET to show cell function and metabolism to offer greater accuracy in the diagnosis and treatment of certain types of diseases, particularly cancer.

If you are pregnant or think you may be pregnant, have kidney disease or have had prior allergic reactions to CT contrast in the past, you should notify your health care provider or technologist prior to the scan.

How is a CT scan performed?

Although each facility may have specific protocols in place, CT scans generally follow this process:

  1. When the patient arrives for the CT scan, he or she will be asked to remove any clothing, jewelry, or other objects that may interfere with the scan.
  2. If the patient will be having a procedure done with contrast, an intravenous (IV) line will be started in the hand or arm for injection of the contrast medication. For oral contrast, the patient will be given the contrast material to swallow.
  3. The patient will lie on a scan table that slides into a large, circular opening.
  4. The CT staff will be in another room where the scanner controls are located. However, the patient will be in constant sight of the staff through a window. Speakers inside the scanner will enable the staff to communicate with and hear the patient. The patient may have a call bell so that he or she can let the staff know if he or she has any problems during the procedure.
  5. As the scanner rotates around the patient, X-rays will pass through the body for short amounts of time. The patient may hear buzzing, whirring, and clicking as the X-ray tube rotates.
  6. The technologist will be watching the patient at all times and will be in constant communication.
  • Preparing for Your CT/CAT Exam

    Read about how to prepare for a CT exam.

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