Positron Emission Tomography (PET) Scan

Positron Emission Tomography Scan (PET) is an imaging test that can help reveal how your tissues and organs are functioning.  To show this chemical activity, a small amount of radioactive material must enter your body.

The precise type of radioactive material, and its delivery method, depends on which organ or tissue is being studied by the PET scan.  The radioactive material may be injected into a vein, inhaled or swallowed.

More radioactive material accumulates in areas that have higher levels of chemical activity.  This often corresponds to areas of disease and shows up as brighter spots on the PET scan.  A PET scan is useful in evaluating a variety of conditions-including neurological problems, heart disease and cancer.

Why it’s done
A PET scan is an effective way to examine the chemical activity in certain parts of your body, which may help detect abnormalities in those areas.


Cancer cells show up as brighter spots on PET scans because they have a higher metabolism rate than do normal cells.  PET scans may be useful in determining:

  • The extent or spread of certain cancers
  • How well the cancer is responding to treatment
  • If the cancer has recurred

Although a radioactive substance is used during a PET scan, the amount of radiation that you’re exposed to is too low to affect the normal processes of your body.

However, this radioactive material might harm the fetus of a pregnant woman or the infant of a woman who is breast-feeding.

How you prepare
A PET scan is usually done on an outpatient basis.  Your doctor will give you detailed instructions on how to prepare for your scan.  Before undergoing the scan, be sure to tell your doctor about any prescription and over-the-counter medications you’re taking, as well as any vitamins and herbal supplements.  If you’re taking certain medications or have certain diseases, such as diabetes, you’ll receive specific instructions before your scan.

A general rule is to not eat anything for 4-6 hours before the scan.  Wear comfortable clothes to your appointment.  You may be asked to change into a hospital gown for the test.  If an area of your body near your bladder needs to be examined, a soft tube (catheter) may be inserted into your urethra to keep urine drained from your bladder during the scan.

Take prescribed medications as usual unless instructed not to do so.

What you can expect
The PET scanner is a large machine that looks a little like a giant doughnut standing upright, similar to a CT scan.

You must wait 30 to 60 minutes for the radioactive substance to be absorbed by the organ or tissue to be imaged.  After the specified time has passed, you’ll lie on a narrow table that slides into the PET scanner’s opening. Be prepared to lie still while scan is being performed, usually 20-60 minutes depending on the type of scan.  The test itself is painless, but you must lie very still or the images will be blurred.

If you’re claustrophobic, you may feel some anxiety while positioned in the scanner.  Be sure to tell the nurse or technician about any discomfort.  Medications can help you feel more relaxed.

After the test
In general, there are no restrictions on your daily routine after the test.  However, drink plenty of fluids to help flush the radioactive substance from your body.

Different colors or degrees of brightness on the image from a PET scan represent different levels of tissue and organ function.  A radiologist with special training in reading PET scans interprets the images. The report should be sent to your physician within 1 to 2 days.

Images from other tests, such as those from recent computerized tomography (CT) or magnetic resonance imaging (MRI), may be compared or even combined with those of your PET scan.