PET scan - How a PET scan works

During a positron emission tomography (PET) scan, a substance known as a radiotracer will be passed into your body.

A radiotracer is a radioactive chemical that releases tiny particles called positrons. It is usually injected into a vein or, rarely, it can be inhaled as a gas.

Most PET scanners use a radiotracer called fluorodeoxyglucose (FDG), which is similar to naturally occurring glucose except that it is radioactive. The advantage of using FDG is that your body will treat it in a similar way to normal glucose.

Studying how different parts of the body respond to glucose can provide a great deal of information about the body's processes. For example, cancerous tissue processes glucose in a different way to normal tissue, making FDG an effective way of detecting cancers.

As FDG moves through your body it releases positrons. The positrons quickly break down, releasing energy waves called gamma waves. The PET scanner can detect gamma waves, which show up on a computer screen as a three-dimensional image.

PET scan images can highlight how certain parts of your body break down the radiotracer. Different concentrations of positrons show up as areas of different colours and brightness.

A radiologist is a healthcare professional who is trained to interpret images of the inside of the body. They will look at the images produced by your PET scan and report their findings to your specialist doctor.

PET-CT scanners

PET-CT scanners are a newer generation of PET scanners that also incorporate a computerised tomography (CT) scanner. CT scanners take a series of X-ray images and a computer then assembles each scan into a more detailed image.

Combining both types of scanner enables the PET scanner to provide information about how well a certain part of the body is functioning, while the CT scanner can provide information about the anatomy of the body part (its appearance).

This is very useful because some conditions, such as cancer, can disrupt both the function and appearance of the affected body part.