PET scan - How a PET scan is performed

Positron emission tomography (PET) scans are usually carried out on an outpatient basis. This means you will not need to stay in hospital overnight.

Preparing for the scan

Your doctor will give you instructions about how to prepare for your scan. You will not usually be able to eat anything for four to six hours before the scan and you will be advised to drink plenty of water.

You may also be advised to avoid caffeine for 24 hours before your scan. Eating and consuming caffeine could change how your body responds to the radiotracer (radioactive substance), which could make the result of your scan unreliable.

The scan procedure

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

Before having the scan, a radioactive substance known as a radiotracer will be passed into your body.

Depending on the part of your body being scanned, this can either be done by injecting the radiotracer into a blood vessel or breathing it in as a gas. The radiotracer can take 30-90 minutes to travel around your body.

When you are ready to have the scan, you will be taken to the room where the PET scanner is located. You will be asked to lie on the bed of the scanner, which will be moved into the centre of the scanner.

During the scan, you will need to stay still and will be asked not to talk. Depending on the part of your body being scanned, the procedure will take 30-60 minutes.

The scan should not be painful, but if you feel unwell there is a buzzer you can press to alert the medical team in charge of your care. The medical team will be able to see you throughout the scan.

For some people, being inside the scanner can be an unpleasant and claustrophobic experience. Inform your care team before the day of the scan if you have a previous history of claustrophobia (a fear of confined spaces). They may be able to arrange for you to have medication known as a sedative to help you relax during the scan.

After the scan

As a PET scan involves being exposed to a very small amount of radiation, you will not experience any side effects and will usually be able to go home soon after the scan has been completed. If you have had a sedative, you will need to arrange for someone to drive you home after the scan.

You should drink plenty of fluids after the scan to help flush the radioactive medication from your body. The radiotracer should leave your body naturally around three hours after it was given.

The results of your PET scan will be sent from the PET scan department to your specialist. However, it may take a couple of weeks for your specialist to receive the results.

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