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The doctor says you need a PET scan, but what does that mean, exactly? That friendly-sounding acronym stands for “positron emission tomography,” which is a medical diagnostic test using a specialized machine. 

Doctors use PET scans to diagnose cancer, cardiac issues, and central nervous system issues such as dementia and epilepsy.  The scans often pinpoint the precise sites of problems.  Follow-up scans measure the progress of treatment like the growth or shrinkage of cancerous tumors.

The test itself is relatively simple. A medical professional injects a small amount of radioactive dye into a patient’s vein.  The scan then identifies the way body cells react with the pigment. Because abnormal tissues absorb the dye differently from the normal ones, trouble spots show up dramatically in the images the scan produces. 

A patient needs to refrain from eating or drinking anything for several hours before reporting for the analysis.  The medical aide injects the dye and then allows the patient to rest quietly for about an hour while the pigment spreads through the designated areas.  

Following that, a technician instructs the patient to lie motionless on a slab while it moves slowly through an opening in a quiet, round machine. The space inside the device can feel tight, especially for someone who is large or claustrophobic.  Patients may request an anti-anxiety medication.

A PET scan is relatively quiet, although there will be some buzzing and clicking. The machine takes thousands of images during the procedure, which usually takes 30 minutes to an hour to complete. A specially trained doctor then “reads” and interprets the images and sends a report to the patient’s doctor.  Although the test causes no after-effects, the patient is released with a recommendation to drink plenty of water to flush the dye out of their system.  

Physicians also often use the computed (axial) tomography (CAT or CT) scan. CAT and PET scans are similar in many ways, and to the patient, they may seem the same. The machinery and procedures are much alike, and both produce images that require interpretation by specialists.  The differences lie in the information the tests provide to the doctors.  A CT scan gives an idea of how specific areas of the body look inside, while the PET tells how the parts are working. The different information allows the doctors a broader scope of understanding the disease they seek to identify and treat. In fact, many doctors ask for both tests.

Although neither test causes any pain other than a needle prick, they can still be intimidating and sometimes uncomfortable.  A patient needs to know he or she is in good hands.  Both tests are safe, but you can always discuss any concerns or questions with your doctor.