John Lyons, MD

A positron emission tomography (PET) scan is done in a hospital nuclear medicine department or at a special PET center by a radiologist or nuclear medicine specialist and a technologist. You will be asked to lie on a table that is hooked to a large scanner, camera and computer.

The radioactive tracer is usually given in a vein (IV). You may need to wait 30 to 60 minutes for the tracer to move through your body. During this time, you may need to avoid moving and talking.

The PET scanner, which is shaped like a doughnut, moves around you. The scanned pictures are sent to a computer screen so your doctor can see them. Many scans are done to make a series of pictures. It is very important to lie still while each scan is being done. At some medical centers, a CT scan will be done at the same time.

For a PET scan of the brain, you will lie on a bed. You may be asked to read, name letters or tell a story, depending on whether speech, reasoning or memory is being tested. During the scan, you may be given earplugs and a blindfold (if you do not need to read during the test) to wear for your comfort.

If you are having a PET scan of your heart, electrodes for an electrocardiogram (EKG, ECG) will be put on your body.

During the test, you will be alone in the scanner room. The technologist will watch you through a window and you will be able talk to him or her through a two-way intercom at all times.

The test takes 1 to 3 hours.

After the test, drink lots of fluids for the next 24 hours to help flush the tracer out of your body.

Many women have questions about the effect of ultrasounds on unborn babies. Watch as Dr. Oz discusses the safety of ultrasounds and babies in this video.

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A functional magnetic resonance imaging (fMRI) scan can help diagnose diseases of the brain and may also enable doctors to get a better understanding of our mental processes. It may even be possible for a fMRI to detect if we are telling the truth.