Radiation levels used with CAT (computed axial tomography) scans are higher than those used with x-rays. Although some patients are concerned about radiation exposure from a CAT scan, they should weigh the potential risks against the potentially life-saving benefits of the information obtained from the test.

In rare cases, the special dye (contrast medium) used during a CAT scan may cause an allergic reaction in the form of mild itching or hives (small, raised, reddened areas of skin). In more severe reactions, shortness of breath and swelling of the throat or other body areas may occur. Patients who notice any of these symptoms developing during the procedure should immediately alert the technician performing the test.

Patients should also inform the physician of the following before the test:

• Pregnancy. Another exam will likely be substituted to reduce the risk of exposing the fetus to radiation.
  
  
• Asthma or allergies. Contrast mediums can produce allergic reactions in some people, especially those with a history of asthma or certain allergies (e.g., iodine, shellfish, strawberries).
  
  
• Other medical conditions. Certain medical conditions also may increase the likelihood of an allergic reaction to contrast mediums. These include:
  
• • Diabetes
    
  • Heart disease
    
  • Kidney problems
    
  • Thyroid conditions