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What is a PET scan, and are there risks?

A positron emission tomography, also known as a PET scan, uses radiation to reveal cellular activity within the body.

This is most commonly used in cancer therapy, neurology, and cardiology.

Combined with a CT or MRI scan, a PET scan can produce multidimensional, color images of the human body’s inner workings.

It not only reveals what an organ looks like but how it functions.

A PET scan is used to identify certain disorders of health, to schedule care, to assess how an current disease progresses and to see how successful a medication is.

Important facts about PET scans

  • PET scans are often used to diagnose a condition or to track how it is developing.
  • Used alongside a CT or MRI scan, it can show how a part of the body is working.
  • PET scans are often used to investigate epilepsy, Alzheimer’s disease, cancer, and heart disease
  • A scan is not painful, but patients should not consume any food for at least 4 to 6 hours before a scan. They should drink plenty of water.

How it works

Pet scan
PET scans demonstrate the physical state and function of organs.

A computer measures radiation, released by a radiotracer, in a PET scan.

A radiotracer consists of radioactive material which, like glucose, is attached to a natural chemical.

This radiotracer is injected into the body, where it travels to energy-consuming cells consuming glucose.

The more energy a group of cells requires, the more the radiotracer at that position can build up. This will show up on computer-reconstructed images.

The cells, or activity, will show as “hot spots” or “cold spots.” On a PET scan the active areas are bright.

These are known as “hot spots.” Where cells need less energy, the areas would be less bright. They are “cold spots.”

Cancer cells are very involved in the use of glucose relative to normal cells, and a glucose-made radiotracer light up areas of cancer.

The image created on the screen will be analyzed by a radiologist and a doctor will report the findings.

Fluorodoxyglucose (FDG) is an example of a glucose dependent radiotracer. In FDG, molecules of radioactive fluoride are labelled to create a radiotracer by glucose. FDG is the most commonly used radiotracer today.

Oxygen can be used, rather than glucose.


A doctors and his patient
PET scans are an important part of the diagnostic process in cancer and epilepsy, and can directly inform the next stage of treatment.

PET scans are also combined with CT or MRI scans to help make a diagnosis or to collect more details about a health condition and any medical progress.

Whereas an MRI or CT scan reveals how body part looks, a PET scan will help to demonstrate how it functions.

PET scans are widely used to study different conditions.

Epilepsy: It will show which part of the brain causes epilepsy.

It can help doctors determine which care is most suitable, and it can be useful if surgery is required.

Alzheimer’s disease: PET scans may help identify Alzheimer’s disease through assessing sugar intake in different brain regions.

Brain cells that have Alzheimer’s affect appear to use glucose more slowly than normal cells.

Cancer: PET scans will reveal a cancer’s existence and stage, demonstrate whether and where it has spread and help doctors decide on the treatment.

A PET scan can provide an indication of how well chemotherapy works, and a recurrent tumor can be identified earlier than other techniques.

Heart disease: A PET scan can help detect weakened or scarred parts of the heart, and can help identify circulation problems in the heart’s function.

Such knowledge can aid in the planning of heart disease treatment options.

Medical research: Scientists can learn valuable information using PET scans, in particular about brain functioning.

Differences between PET, CT, and MRI scans

A CT or MRI scan can determine the size and shape of body organs and tissue, but can’t measure how these work.

A PET scan will demonstrate how an organ functions but it can be difficult to determine the exact position of activity inside the body without a CT or MRI image.

A PET scan combined with a CT scan will provide a more detailed image of the patient’s situation


Example of pet image scan
PET images show the active cells as bright or ‘hot’ spots.

In general, a PET scan is an outpatient treatment.

The patient does not usually eat any food for at least 4 to 6 hours before the scan but should drink plenty of water. They may need to stop coffeine at least 24 hours before scanning.

First, a small volume of radiotracer would be administered into a vein by the doctor Also, the tracer may be breathed in as a gas, taken by mouth or directly injected into an organ.

Depending on which organ is involved, it may take the radiotracer 30-90 minutes to reach the targeted body part.

Meanwhile, the patient is usually told to stay quiet and not speak. Some patients can receive calming medication.

The patient is likely to need to wear a robe, and will need to remove jewelry.

When the patient is ready for the scan, they are taken to a different room scan. They’ll lie on a cushioned test table.

The table slides into a large hole to encircle the patient.

Patient will stay as calm as possible. They may be able to listen to the music.

The computer takes pictures during the scan.

This will take about 30 minutes depending on which part of the body is being scanned.

It’s not even uncomfortable. If the patient feels unwell, they may press a buzzer to alert the workers.

During the scan a professional doctor must look at the patient.

Usually, the whole testing process takes about 2 hours. Most patients are permitted to go home once the scan is complete.

Patients can eat plenty of water to wash the toxic substances out of their body quicker. The radiotracers would have left the body in 3 to 4 hours, absolutely.


Exposure to radiation runs a risk.

The benefits of getting a PET scan, for most people, outweigh the risks.

However, it is not appropriate for everyone since a PET contains radioactive material.

A pregnant woman does not usually have a PET scan, because the radioactive material may affect the fetus or the baby.

If a woman is breastfeeding, she will follow directions for breast milk pumping and discarding, and ask the doctor when it is appropriate to restart breastfeeding based on the test completed.

Any woman who is pregnant or breast-feeding will immediately inform her doctor before getting a PET scan.

A patient may be advised to remain away from pregnant women, babies, and young children for a few hours after a PET scan, as the radioactivity presents a slight risk.

An individual can very rarely have an allergic reaction to the tracer.

Chukwuebuka Martins

Chukwuebuka Martins is a writer, researcher, and health enthusiast who specializes in human physiology. He takes great pleasure in penning informative articles on many aspects of physical wellness, which he then thoroughly enjoys sharing to the general public.