What is a PET scan?

An imaging test called a positron emission tomography (PET) scan provides dynamic pictures of your organs and tissues. This test requires a PET scanner and a radiotracer a harmless, injectable radioactive chemical. The scanner looks for sick cells that absorb too much of the radiotracer to identify a potential health problem.

Healthcare providers often use PET scans to assist with diagnosing cancer and monitor cancer treatment. They can also use the scan to evaluate some heart and brain conditions.

What is the difference between a PET scan, CT scan and MRI?

Computed tomography (CT) scans employ X-rays, while magnetic resonance imaging (MRI) scans employ magnets and radio waves. Both create static images of organs and body structures.

PET scans use a radioactive tracer to reveal an organ's function in real-time. PET scan images can identify cellular changes in organs and tissues much earlier than a CT or MRI scan. Your healthcare provider may order a PET and CT scans (PET-CT). Such a dual imaging test produces 3D images that make a more accurate diagnosis possible.

Some hospitals offer hybrid PET/MRI scans, which use new technology to provide high-contrast images. Providers primarily use this type of scan to diagnose and monitor cancers of the soft tissues (brain, head and neck, liver, and pelvis).

What is checked on a PET scan?

A healthcare provider might order a PET scan to look for evidence:

• Cancer, including breast cancer, lung cancer, and thyroid cancer.
• Coronary artery disease, heart attack, or other heart problems.
• Brain disorders, including brain tumours, epilepsy, dementia, and Alzheimer's disease.

When may I need to undergo a PET scan?

A PET scan measures vital functions such as blood flow, oxygen use, and metabolism of blood sugar, called glucose. It can also detect organs and tissues that aren't functioning correctly.

You may have to undergo a PET scan if your doctor suspects you have cancer. A PET scan can identify the presence of cancer or even determine a diagnosis.

If you are diagnosed with cancer, your doctor may order PET scans repeatedly throughout your course of treatment to:

• Confirm whether the cancer has metastasized in your body.
• Evaluate the efficacy of your treatment
• Establish whether there is a recurrence of cancer
• Provide an estimate of the prognosis of your cancer.
• If you're having heart problems, your doctor may suggest a PET scan to assess the effect of a heart attack on different parts of your heart.
• Identify the cardiac muscle regions that will benefit from angioplasty or coronary artery bypass operations.
• If you have neurological symptoms, your doctor may suggest a PET scan to assess any possible brain abnormalities, including tumours, seizures, and other disorders affecting the central nervous system.

How does a PET scan work?

A PET scan is a type of nuclear medicine image. Nuclear medicine uses minute and safe amounts of radioactive material, called radiotracers, which are administered through an IV.

Unlike other imaging techniques, PET scans focus on processes and molecular activity in your body. This gives them the potential to find disease in its very earliest stages.

Abnormal cells in your body take up more of the radiotracer than normal cells. These are referred to as "hot spots." The radiation sent out by these areas is detected by the PET scanner, which creates images of the affected tissue. A PET/CT scan integrates X-ray images from a CT scan with PET scan images.

How do I prepare for a PET scan?

PET scans can be performed as an outpatient procedure, meaning you can go back home the same day. Your healthcare provider will tell you how to best prepare for the scan. In general, you should make sure that the provider has the latest list of all medications, vitamins, or supplements you are taking and any allergies that you may have. Also, inform your provider if you might be pregnant or if you are breastfeeding.

• Do not eat anything for six hours before the test. Your healthcare provider may modify this instruction if you have diabetes.
• Only drink water.
• Do not have caffeine 24 hours before the test if you are being tested for heart disease.
• Wear comfortable clothing and leave any metal items like jewellery, eyeglasses, dentures, and hairpins at home.

Let your doctor know if you feel claustrophobic about an enclosed space. You can take a mild sedative before the test to help you relax.

What happens during a PET scan?

The following is what you might expect during a PET scan:

You will be given an intravenous injection of a radiotracer containing a small amount of a radioactive substance. The radiotracer fluorodeoxyglucose (FDG) is most commonly used. For about an hour, you will remain seated in a chair as the radiotracer passes through your bloodstream and is absorbed by your organs and tissues. You need to remain relatively still so that the radiotracer does not wander to areas of your body that your healthcare provider is not testing. You cannot feel the radiotracer.

• If you are having a PET/CT scan, a contrast dye might be injected into a vein through an IV. The dye helps create clearer images from the CT scan.
• You lie on an exam table that moves in and out of the PET/CT scanner. This doughnut-shaped machine has a tunnel opening that is about 30 inches in diameter.
• It would help if you were immobile for the scan, about 30 minutes. You should be relatively still since movement can blur the images.
• You will hear humming and clicking sounds as the scanner takes pictures.
• A technologist will evaluate the scans before you leave to ensure the images are clear.

How long does a PET scan take?

The whole time required for the PET scan is roughly two hours.

The injected radiotracer may take up to 60 minutes to be absorbed by your body. During this period, you must sit quietly and move as little as possible. The PET scan itself takes around half an hour. You will have to wait after the screening while the technician checks the scans to make sure the pictures are clear.

What are the risks and side effects of a PET scan?

In general, PET scans are safe and cause few problems. The amount of radiation in the radioactive tracer is minimal. It stays in your body for a short time. After a PET scan, you should drink lots of water to flush the radioactive drug out of your body.

Generally, PET scans pose risks only under the following conditions:

• Pregnant, breast-feeding or chest feeding people should not take PET scans. The radiation may pose harm to a fetus and can be transferred to an infant via breast milk.
• Some people are allergic to the radioactive tracers given with a PET scan or to the dyes used in contrast with a CT scan. Such allergic reactions are infrequent and usually relatively mild. Your medical team can administer medication that will rapidly slow and stop this response if it occurs.
• The sugars in the radiotracer cannot be absorbed by diabetics, which can alter the scan findings. Your doctor will advise you to change your medication and diet before the test.

When can I expect my PET scan results?

After looking at the images, a radiologist with particular skills in PET scans will write a report and send it to your healthcare practitioner. This process usually takes a full day.

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