A positron emission tomography (PET) scan is used to give doctors a three-dimensional view inside a person's body.
The PET scan shows the part of the body being scanned and how well it is working.
Uses of PET scans include identifying part of the brain that is causing seizures in a person with epilepsy, or problems in the brain caused by dementia.
A PET scan may be performed to plan an operation, such as heart surgery, or to monitor cancer, or other treatment.
How a PET scan works
The PET scan is done by injecting a small amount of radioactive material, called tracer, into a vein, usually in the arm.
Positively charged particles called positrons in the tracer interact with negatively charged particles called electrons in the body.
The PET scanner uses this interaction to form an image.
Not all hospitals will have PET scanners, so a referral to a specialist centre may be made.
Before having a PET scan
Before having a PET scan, the medical team will make sure they know about existing health conditions and medication taken.
Although the amount of radiation involved in a PET scan is at safe levels, it is important for women to say whether they might be pregnant or are breastfeeding, as there are risks in these cases.
The PET scanner will usually have a flat bed to lie on, with the circular scanner at the end.
It is important to stay still and not speak during the scan. You will be monitored from a control room, and will be able to let the operator know if you are distressed or are experiencing discomfort.
The scanner may upset people with a fear of enclosed spaces (claustrophobia), and sedation may be recommended in some cases.
Specific instructions will be given before leaving the scanning centre on drinking fluids to help flush out the tracer.
If sedation has been given, the person will not be able to drive home.
The results of the PET scan will usually be given through the doctor who requested them some days or weeks later.