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For your PET scan, a radioactive drug (tracer) will be put into your body. The amount of radiation you're exposed to is small, and the risk of negative effects from it is low. But the tracer might:

• Cause a major allergic reaction, in rare instances
• Expose your unborn baby to radiation if you are pregnant
• Expose your child to radiation if you are breast-feeding

Talk with your doctor about the benefits and risks of a PET scan.

Tell your doctor:

• If you've ever had a bad allergic reaction
• If you've been sick recently or you have another medical condition, such as diabetes
• If you're taking any medications, vitamins or herbal supplements
• If you're pregnant or think you might be pregnant
• If you're breast-feeding
• If you're afraid of enclosed spaces (claustrophobic)

Your doctor will give you detailed instructions on how to prepare for your scan. A general rule is to avoid strenuous exercise for a couple of days before the study and to stop eating a few hours before the scan.

The PET scanner is a large machine that looks a little like a giant doughnut standing upright, similar to a computerized tomography (CT) machine. You'll need about two hours for the procedure, which may be done on an outpatient basis (no overnight hospital stay). When you arrive for your scan, you may be asked to:

• Change into a hospital gown
• Empty your bladder

Then you will be given a radioactive drug (tracer). You may receive the drug by injection or be asked to inhale or swallow it, depending on the type of tracer being used. If the drug is injected, you may briefly feel a cold sensation moving up your arm. You'll need to wait 30 to 60 minutes for the tracer to be absorbed by your body.

During the PET scan

When you are ready, you'll lie on a narrow, padded table that slides into the scanner. During the scan you'll need to lie very still so that the images aren't blurred. It takes about 30 minutes to complete the test. The machine makes buzzing and clicking sounds.

The test is painless. If you're afraid of enclosed spaces, you may feel some anxiety while in the scanner. Be sure to tell the nurse or technologist about any discomfort. He or she may give you a drug to help you relax.

In some cases you may have a CT and PET scan in the same machine during the same appointment. The CT scan will be done first and take about 10 minutes.

After the PET scan

After the test you can carry on with your day as usual, unless your doctor tells you otherwise. You'll need to drink plenty of fluids to help flush the tracer from your body.

Pictures from a PET scan display bright spots where the radioactive tracer collected. These spots reveal higher levels of chemical activity and details about how your tissues and organs are functioning. A doctor specially trained to interpret scan images (radiologist) will report the findings to your doctor.

The radiologist may also compare your PET images with images from other tests you've undergone recently, such as computerized tomography (CT) or magnetic resonance imaging (MRI). Or the pictures may be combined to provide more detail about your condition.