PET scan

Positron emission tomography (PET) scans are used to produce detailed three-dimensional images of the inside of the body.

The images clearly show the part of the body being investigated and can highlight how effectively certain functions of the body are working.

What PET scans are used for

PET scans are often used to help diagnose a range of different cancers and work out the best ways of treating them. The PET scan can show how far a cancer has spread or how well it is responding to treatment.

Sometimes PET scans are used to help plan complex heart surgery, such as a heart transplant. They can also be used to help diagnose a number of conditions that affect the normal workings of the brain (neurological conditions), such as dementia.

Read more about why PET scans are used.

How PET scans work

PET scanners have a flat bed with a large, circular scanner at one end.

Before you have a PET scan, a radioactive substance (a radiotracer) will be passed into your body. This is usually by injection into a vein.

The tracer gives off particles called positrons that release gamma waves (a type of radiation), which can be detected by the PET scanner.

By tracking the movement of the tracer, the scanner can build up a detailed image of a number of the body's functions, as well as identifying areas of the body that have been affected by disease.

Read more about how PET scans work and what happens during a PET scan.


As PET scanners are expensive, they are usually only found at larger hospitals and some specialised research centres.

Because of the lack of availability, PET scans tend to only be recommended for people with complex health problems. They are not routinely used to diagnose cancer, but are often used in confirmed cancer cases to see how far the cancer has spread and whether treatment has been effective.

However, PET scans are becoming more widely used by the NHS, with an average of 40,000 PET scans being carried out by the NHS in England each year.


Any exposure to radiation carries a very small risk of causing damage to tissues and the possibility of triggering a new cancer.

However, in a standard PET scan the amount of radiation you are exposed to is the same as the amount received from natural sources, such as the sun, over the course of three years.

Increasingly, PET scans are being combined with computerised tomography (CT) scans to provide more detailed images.

These new types of scanners, known as PET-CT scanners, use higher levels of radiation, which are equivalent to the recommended levels that someone working in a nuclear power plant should be exposed to over the course of a year. However, this dose is still well within the acceptable safety limits for radiation exposure.

Read more about the possible risks of PET scans.

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