A CAT (computed axial tomography) scan, or CT scan, is a noninvasive imaging test that uses multiple x-ray images, taken from different angles, to create three-dimensional images of body structures. It may be performed alone or with the use of a special dye (contrast medium). CAT scans often employ digital x-rays to produce images on a computer screen.

CAT scans are used to diagnose numerous injuries, conditions and diseases, including those that affect the digestive system. In particular, CAT scans are used to examine damage or inflammation to organs such as the pancreas, liver, rectum and colon.

They can also be used to determine the progress of a previously diagnosed disease. Problems that may be detected with a CAT scan include:

• Internal injuries or bleeding
• Muscle and bone disorders, such as osteoporosis
• Tumors, infections or blood clots
• Diseases, such as cancer or cirrhosis
  

  

CAT scans may also be used to plan radiation treatment for tumors, to guide biopsies and to plan surgery.

Of all the imaging tests that are currently available, the CAT scan is best able to produce images of bone, blood vessels and soft tissues. Therefore, it is generally the test of choice when examining patients who have been injured (e.g., as the result of a car collision or sports injury).

A CAT scan can provide detailed images of nearly every part of the body, including:

• The abdomen, including the liver, kidney, spleen, pancreas and other abdominal organs
  
  
• The rectum
  
  
• The chest (thoracic CAT scan), including the heart, aorta and lungs
  
  
• The head, including the brain, vessels of the brain, eyes, inner ear and sinuses
  
  
• The back, including the entire spinal column
  
  
• The neck, including the shoulders, cervical spine and blood vessels of the neck
  
  
• The pelvis and hips, including the bladder and gastrointestinal tract
  
  
• The skeletal system, including bones of the hands, wrists, feet, ankles, legs, arms and jaw

An increasing number of people in the United States are choosing to have preventive CAT scans performed on an annual basis. These full-body CAT scans are designed to detect certain diseases in very early stages, but the value of these tests is considered highly controversial among medical experts.

Critics contend that the scans will mostly detect conditions that are ultimately benign. Another concern is that individuals may think a preventive scan is a suitable alternative to regular physical examinations with a primary care physician.

It has been suggested that preventive CAT scans be reserved for higher risk individuals, as opposed to healthy, asymptomatic (without symptoms) people younger than age 40 without a family history of heart disease, cancer or other diseases.

Because a CAT scan involves x-rays, pregnant women should not have abdominal or chest CAT scans. If the use of a special dye (contrast medium) is recommended during the test, then individuals should report any history of blood-clotting disorders or allergic reactions to any of the following:

• Iodine
• Shellfish (e.g., crab or shrimp)
• Strawberries
  

Research indicates that milk may be nearly as effective as some contrast agents (e.g., barium) for abdominal CAT scans. In the future, this may prove a less expensive, safer and more palatable alternative for some patients.