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 cross-sectional images (often called slices), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than standard x-rays. CT scans also minimize exposure to radiation.

In standard x-rays, a beam of energy is aimed at the body part being studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle, and other tissue. While much information can be obtained from a regular x-ray, a lot of detail about internal organs and other structures is not available.

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 that interprets the x-ray data and displays it in 2-dimensional form on a monitor. Newer technology and computer software makes three-dimensional (3-D) images possible.

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. Your physician will notify you of this prior to the procedure.

CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage.

Advances in computed tomography technology include the following:

• high-resolution computed tomography
  This type of CT scan uses very thin slices (less than one-tenth of an inch), 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, with the x-ray beam circling the patient. 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.
• ultrafast computed tomography (also called electron beam computed tomography)
  This type of CT scan produces images very rapidly, thus creating a type of "movie" of moving parts of the body, such as the chambers and valves of the heart.
• computed tomographic angiography (CTA)
  Angiography (or arteriography) 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.
• 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.

You will need to let your physician know if you have ever had a reaction to any contrast dye, or if you are allergic to iodine or seafood. If you are pregnant or think you may be pregnant, you should notify your physician. If you are claustrophobic or tend to become anxious easily, tell your physician ahead of time, as he/she may prescribe a mild sedative for you before the procedure to make you more comfortable. It will be necessary for you to remain still and quiet during the procedure, which may last 10 to 20 minutes, on average.

Reminders Before the ExaminationTell the radiologist if you are allergic to iodine or other materials, if you are pregnant, or if you are claustrophobic and think you will be unable to lie still while inside the scanning machine.

How is a CT or CAT scan performed?

CT scans can be performed on an outpatient basis, unless they are part of a patient's inpatient care. Although each facility may have specific protocols in place, generally, CT scans follow this process:

1. When the patient arrives for the CT scan, he/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 medication to swallow.
3. The patient will lie on a scan table that slides into a large, circular opening of the scanning machine.
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 will have a call bell so that he/she can let the staff know if he/she has any problems during the procedure.
5. As the scanner begins to rotate around the patient, low-dosage x-rays will pass through the body for short amounts of time.
6. The x-rays absorbed by the body's tissues will be detected by the scanner and transmitted to the computer.
7. The computer will transform the information into an image to be interpreted by the radiologist.
8. It is very important that the patient remain very still during the procedure.
9. The technologist will be watching the patient at all times and will be in constant communication.
10. The patient may be asked to wait for a short period of time while the radiologist examines the scans to make sure they are clear. If the scans are not clear enough to obtain adequate information, the patient may need to have additional scans performed.