Why a PET scan is used 

Positron emission tomography (PET) scans are usually used in combination with other tests, such as X-rays or magnetic resonance imaging (MRI) scans, to investigate or diagnose health conditions.

PET scans can also be used to find out how well a treatment is working.

Compared with other types of scans, the main advantage of a PET scan is that it can indicate how well a particular part of the body is working, rather than simply showing what it looks like.

PET scans can highlight how a condition has affected the body's functions, and enable healthcare professionals to accurately track how far a condition such as cancer has spread.


One of the most common uses of a PET scan is to investigate confirmed cases of cancer. In particular, a PET scan can usually provide three important pieces of information. These are:

  • how far the cancer has spread – this is known as staging: the higher the stage, the further the cancer has spread
  • how well the cancer is responding to treatment
  • whether any cancerous cells remain after a course of treatment has been completed

Neurological conditions

Less commonly, PET scans are used to help diagnose conditions that can affect the brain and nervous system (neurological conditions).

For example, a PET scan can be used to help plan brain surgery in cases of epilepsy that have not responded to medication.

The PET scanner can sometimes locate damage to the brain that is responsible for triggering seizures (disruption of normal brain activity). The damaged areas of the brain can be removed using surgery.

PET scans can also help diagnose dementia (a group of symptoms related to a decline in brain function) and Parkinson's disease (a condition where part of the brain becomes progressively more damaged, resulting in involuntary shaking).

Heart disease

PET scans are a very effective way of tracking the blood flow in and around the heart. They are therefore often used to determine whether someone could benefit from different types of heart surgery, such as:

  • heart transplant – where a diseased heart is replaced with a healthy heart taken from a donor who has died
  • coronary artery bypass graft – where a blood vessel taken from another part of the body is used to bypass a blocked or narrowed section of artery
  • angioplasty – where a blocked or narrowed section of artery is widened using a small metal tube called a stent

Medical research

PET scans can also be used to look at how the body works and to help understand what happens when something goes wrong with the way the body functions.

For example, researchers are currently using PET scanners to study the brain function of people with autism (a range of related developmental disorders that affect language development and social interaction).

When PET scans are not recommended

A PET scan may not be suitable if you have chemical imbalances in your body.

For example, the scan may give false results if you have poorly controlled diabetes.

Page last reviewed: 07/03/2013

Next review due: 07/03/2015