Patient education: PET scan (The Basics)

What is a PET scan? — 

PET stands for "positron emission tomography." It is a type of imaging test that creates pictures of the inside of the body (figure 1). A PET scan can show changes and problems earlier than other imaging tests, like CT or MRI.

For a PET scan, a chemical called a "radioactive tracer" is injected into 1 of your veins. It travels through your bloodstream and is absorbed by your organs, tissues, and bones. Then, a scanner with a special camera takes pictures. If the scan shows "hot spots," these are areas where the tracer built up more in some of your cells. They can be a sign of disease or another problem.

A PET scan can also be done along with a CT or MRI scan. The images from the CT or MRI can create a 3-D image of the scanned area. This can be combined with the images from the PET scan to give doctors more information:

●PET/CT scans are often used to look at organs, tissues, and bones.

●PET/MRI scans are often used to look at soft tissues.

Why do I need a PET scan? — 

PET scans can be used to look at different areas of the body, such as the:

●Brain and spine

●Organs in the chest, belly, or pelvis

●Heart and blood vessels

●Soft tissues like lymph nodes

●Bones

The scan can look for problems in a specific part of the body, monitor a known condition, or check if treatment is working. Doctors can use a PET scan to:

●Find cancer cells, see if cancer has spread or come back, or see how treatment is working

●Look for inflammation

●Learn more about blood flow to the heart and how well the heart is working

●Find and monitor problems in the brain

How do I prepare for a PET scan? — 

The doctor or nurse will tell you if you need to do anything special to prepare.

Before the scan, your doctor will do an exam and ask about your "health history." This involves asking you questions about any health problems you have or had in the past, past surgeries, and any medicines you take. Tell them about:

●Any medicines you are taking – This includes any prescription or "over-the-counter" medicines you use, plus any herbal supplements you take. It helps to write down and bring a list of any medicines you take, or bring a bag with all your medicines with you.

●Any allergies you have

●Any metal in your body – This includes medical devices like pacemakers, artificial joints, ear implants, or IUDs (a type of birth control). It also includes any hardware like pins, screws, metal plates, or staples that might have been put in during surgery (for example, to fix a broken bone). Metal can interfere with the images from the scan.

●Any other devices or materials on your body – These include things like insulin pumps, medicine patches, piercings, and dentures. You will also be asked if you have any tattoos or permanent makeup. These can affect the images as well.

●Whether you could be pregnant or are breastfeeding – A PET scan can be done during pregnancy if needed. But your doctor might want to delay the scan until after you give birth. If you are breastfeeding, tell your doctor.

●If you get nervous in small spaces – Some PET scan machines are narrow. If small spaces make you feel nervous or anxious, tell your doctor. If needed, they can give you medicine to help you stay calm during the scan. If you cannot lie still for the entire test, your doctor will talk to you about other options, such as sedation.

You will also get information about:

●Eating and drinking before the scan – You might need to "fast" before the scan. This means not eating or drinking anything that has sugar or dextrose for a period of time. You might also be asked to avoid caffeine, alcohol, or nicotine. You can usually have water until a short time before the test. If you have diabetes, talk with your doctor about whether you should take your medicines before the test.

●If you need to take medicine to empty out your stomach or bowels before the test

●If you need to avoid exercise for a day before the test

Ask the doctor or nurse if you have questions or if there is anything you do not understand.

What happens during a PET scan? — 

When it is time for the test:

●You might change into a hospital gown. You will remove any metal objects from your body, like jewelry, glasses, dentures, and hearing aids.

●You might get an "IV," which is a thin tube that goes into a vein. This can be used to give you the tracer and medicines. The staff might also place a catheter in your bladder to drain urine during the test.

●If needed, you might get medicines to make you relax and feel sleepy, called "sedatives."

●The staff might need to check your blood glucose (blood sugar).

●The person doing the CT scan (called a "technologist") will use your IV to inject the tracer into your vein. You might need to drink a special liquid. You might also get a special dye, or "contrast," injected into your vein during the test.

●You will lie on the narrow table of the scanner. The table slides into the machine. The technologist will not be in the room with you, but they will be nearby and can see you and talk to you.

●You will need to lie very still as the tracer moves through your body. This is so the images will be clear. You might also be asked to do things, like hold your breath for a few seconds. The machine does not touch you, and the test does not hurt.

●When the scan is over, the table will slide back out of the machine.

●A PET scan usually takes about 30 minutes. The whole test can take between 1 and 3 hours, including the time it takes for the tracer to move through your body.

What happens after a PET scan? — 

If you had an IV or bladder catheter, it will be removed. In most cases, you can go home right away.

The tracer is radioactive. For the next 1 to 2 days, or as instructed by your doctor:

●Drink plenty of water to help your body get rid of the tracer, unless your doctor told you otherwise.

●Your body will get rid of the tracer on its own through urine or bowel movements. When you use the toilet, flush twice, and wash your hands thoroughly. This helps prevent other people from being exposed to the tracer.

●Even though the amount of radiation is very small, you might need to avoid being around pregnant people and children for a period of time.

●If you are breastfeeding, feed your baby before the test. After the test, you will need to stop breastfeeding for a period of time. During this time, you can pump or express milk and then throw it away. Follow your doctor's recommendations for how long to stop breastfeeding.

If you got medicine to help you stay calm during the scan, someone will need to bring you home afterward.

What are the risks of a PET scan? — 

Your doctor will talk to you about all the possible risks, and answer your questions. Possible risks include:

●Allergic reaction to the tracer (this is rare)

●Allergic reaction to the contrast, if it was given

●Radiation exposure – A PET scan exposes you to some radiation. In general, exposure to radiation very slightly raises your risk of developing cancer later in life. But the amount of radiation during a PET scan is very small. The overall risk increases if you have to get many scans over time.

What else should I know? — 

You might get your results the same day, or it might take a little longer for an expert to review them. Your doctor or nurse will tell you when to expect your results.

If your PET scan shows any abnormal results, your doctor or nurse will talk to you about what to do next.

More on this topic

Patient education: CT scan (The Basics)
Patient education: MRI scan (The Basics)