What Is a PET Scan and Why You Might Need One

What is a PET scan? If a doctor recommends a PET scan for you or your loved one, you may wonder what’s in store for you. So it may help you to understand exactly what it is.

You may already be familiar with PET scans from movies and TV shows. But the reality may be a little different.

So keep reading to find out exactly what a PET scan is, as well as what it’s used for. Also, find out what to expect from a PET scan and the possible risks.

What Is a PET Scan?

PET or positron emission tomography scan is an imaging test that doctors run to check for diseases. However, it doesn’t just give an image. It also shows how the organs are functioning.

You may think that PET scans just let doctors know if there is a disease present. But doctors also use the information from these scans for other purposes, such as planning treatments, monitoring a condition, and even verification of how the treatment is going.

These scans can also measure a variety of body functions such as:

  • blood flow
  • oxygen use
  • blood sugar use

MRI and CT scans are sometimes used in conjunction with PET scans to give the doctor a comprehensive picture of a person’s health.

What Is It Used For?

PET scans can show potential problems at a cellular level. So this helps doctors detect complex systemic diseases like:

  • heart problems
  • brain conditions
  • cancer

This is possible because a special dye that has radioactive tracers is used when scanning. The tracers are inhaled, swallowed, or injected into an arm vein to tint your organs. How the tracer is introduced depends on what area of the body your doctor wants a closer look at.

These tracers are then absorbed into the organs and tissue. Tracers collect in areas that have a high level of chemical activity. And certain tissues and diseases have higher levels of activity than others.

For example, there’s a high level of chemical activity in cancerous cells. So these cancer cells show up brightly on PET scans. Because of this, doctors can use this scan to:

  • track cancer progression
  • treatment effectiveness
  • cancer reoccurrence

Looking at scans to track a patient’s cancer progression, however, isn’t fool-proof. Sometimes non-cancerous cells look like cancer cells in the scans. Also, tumors sometimes don’t show up on PET scans at all.

Furthermore, these scans may also help diagnose and treat a variety of central nervous disorders like:

  • depression
  • epilepsy
  • Alzheimer’s disease
  • Parkinson’s disease
  • head trauma


PET scans are generally outpatient procedures, so patients can go about their day after one is performed. And they are generally not painful. But having one does require a little prep work a few hours prior to the scan.

You’ll receive a tracer prior to the scan. This may take up to an hour because your body needs time to absorb the tracers. However, the actual time may differ depending on the area of the body the scan is performed on.

Hospital personnel may advise you to limit your movements and try to stay relaxed as the tracer is absorbed. If you’re getting a brain scan, you may want to avoid stimulating activities like reading, television, and music, too.

The scan itself can last between 30 to 45 minutes. The PET scan technician will also direct you to remain still when needed. You may also be asked to hold your breath for a few seconds. And it’s not uncommon to hear clicking and buzzing noises while the machine is scanning.

Possible Risks and Precautions

The idea of receiving radioactive tracers may not sound like a good idea to you. However, the actual exposure to harmful radiation is low. If you’re still concerned, you may want to speak with your doctor about the possible risks.

Because tracers contain radioactive material, it’s generally not a good idea for pregnant women to have PET scans. Women who are breastfeeding may also want to pump and discard any breast milk until the doctor says otherwise. This is to limit potential radioactive contamination passing to the baby.

Occasionally, an individual may have an allergic reaction to the tracer. It rarely happens, though. But if you are allergic to aspartame, iodine, or saccharin, you should let your doctor know right away.

People who are allergic to iodine may have an alternative tracer. Some conditions may come with increased risks of an allergic reaction:

  • asthma
  • allergies
  • dehydration
  • heart disease
  • kidney disease
  • blood cell disorders
  • certain drug regimens
  • prior allergic reactions to the scan

Other considerations are possible discomfort if you are claustrophobic because the scan is done in a tight, enclosed space. Additionally, if you are uncomfortable with needles, you may be leery about receiving tracers via injection.

After a PET Scan

Once a PET scan is complete, you can leave the facility unless your doctor says otherwise. Keep in mind, however, that the radioactive material can remain in your body for up to 12 hours. Because of that, patients may also be advised to stay away from infants, young children, and pregnant women for a few hours. Any radioactivity is minimal but it may still pose a small risk.

Furthermore, the tracers should leave your body within a couple of days. But drinking a lot of fluids can help to flush them from your system.

A trained specialist may go over the PET scan with your doctor, but it can take a couple of days for you to receive the results. Your doctor will go over those results with you at your follow-up appointment.

Final Thought

Being told that you need a PET scan may seem intimidating. But there’s no reason to get anxious. Around 2 million PET scans are performed in the U.S. each year. And it’s a relatively standard procedure at most medical centers.

If you still feel anxious or have other concerns, speak with your doctor. They may provide additional information that can alleviate any lingering fears.