PET Scans: The Procedure, Risks, Indications, and More

Wondering what a PET scan is? Here is your quick guide to what it is, its indications, risks, how it’s done and more.

What is a PET scan?

A PET scan or Positron Emission Tomography scan is a special type of imaging technique used to assess the metabolic or biochemical function of your cells and organs. A dye that contains radioactive tracers is administered to the body, usually as an injection. The tracer gets distributed in the body through the blood and any abnormality can be detected based on the variations in the distribution of the tracer.

Why is a PET scan done?

To diagnose cancer and analyse its metastatic spread, identify organs exhibiting suboptimal function, and assess specific brain disorders such as Alzheimer’s disease and certain tumors.

What are the risks of a PET scan?

A PET scan may expose you to a mild amount of radiation. Although the risk from this radiation is low, if you’re pregnant, it may expose your unborn child to radiation. Additionally, if you are breastfeeding, your breastfed child can get exposed to radiation through the breast milk. There is also a mild risk of an allergic reaction to the dye.
PET scan

How do I prepare for a PET scan?

If you’re advised to undergo a PET scan, you should inform the your doctor in advance about any history of allergies, medical history of any significant ailments such as diabetes, and the list of medicines that you take. You also need to inform the doctor if you suspect that you are pregnant, if you are breastfeeding, or if you have claustrophobia.

If you are scheduled to undergo a PET scan, your doctor will give you detailed instructions on how to prepare for the scan. These instructions usually include:

  • You will be advised to refrain from strenuous exercises for a few days before the procedure
  • You will be advised to stop eating for 4 to 6 hours before the procedure

What happens during a PET scan?

Before the scan, you will be asked to switch from your regular clothing to a hospital gown and to empty your bladder.

You will be injected with the tracer and will be asked to wait for nearly an hour for the tracer to get absorbed and distributed in the body.

After this, you will be asked to lie down on a bed in the scan room. The bed slides into the scanner, which is shaped like a tunnel, where your scanning is done.

To improve the diagnostic quality of the final image, a PET scan is usually combined with a CT or MRI. PET/CT usually takes around 30 minutes, and PET/MRI usually takes around 45 minutes to complete. You will have to stay still during the entire procedure.

If you have claustrophobia, inform your doctor in advance. You can keep your eyes closed or listen to music to overcome the claustrophobia. If your condition is severe, the doctor may prescribe mild sedatives to help you relax.

Following the procedure, you will be discharged from the scan room and advised to drink plenty of water to flush out the tracer from the body.

Your radiology specialist will issue a report after studying the computer-generated images carefully.

What differentiates a PET scan from a CT or MRI scan?

CT and MRI scans detect any change in the structure and appearance of various tissues in the body. The X-ray radiation in the case of CT and the magnetic field in the case of MRI originate outside the body. A PET scan ,on the other hand, shows the functional and biochemical status of the body structures. The source of energy originates through the breakdown (radioactive decay) of the tracer, which is within the body of the person who is being scanned.

The changes in the functional and biochemical properties begin much before there are any evident changes in the appearance of the tissues. Hence, PET scans can detect abnormalities at a much earlier stage than CT or MRI.

Will undergoing a PET scan during pregnancy affect my baby?

PET scans are usually not advised during pregnancy. However, if the scan is inevitable for diagnosis, you should not refuse it. Past research has revealed that the amount of radiation to the baby in the womb of a mother who is undergoing a PET scan is very minimal, and they are born without any visible defects. Your doctor would advise a PET scan during pregnancy only if the benefits outweigh the risks. However, you must inform the doctor in advance if you are pregnant.
Dr. Sosa

Dr. Sosa


An oral physician turned medical writer who writes profoundly about medicine and diseases. Read her contributions and writings about various healthcare topics.

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