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A PET CT scan helps doctors see how your body's cells are working and can show if there's any unusual activity. This test uses a small amount of a harmless radioactive substance to help create these images.

The name "PET CT" stands for Positron Emission Tomography - Computed Tomography. It combines these two imaging methods to give a detailed picture of what's happening inside your body.

There are many reasons you might need a PET CT scan. Some common ones include:

  1. Checking for cancer or monitoring its progress.
  2. Finding out if a cancer treatment is working.
  3. Investigating problems with your heart or brain, like heart disease or memory issues.
  4. Helping doctors plan surgery or other treatments.
  5. Checking for infections or inflammation in your body.

PET CT scans are an important imaging tool for the diagnosis and treatment of cancer, heart disease and brain disorders. PET stands for Positron Emission Tomography, and CT stands for computed tomography. A PET scan is used to detect overactivity in certain parts of the body, while a CT scan provides detailed information about the position of this activity in various organs or structures inside the body. When combined, these two scans provide valuable diagnostic information, enabling doctors to make more informed decisions about treatments.

PET CT scans involve injecting a small amount of radioactive material into the body. This material is then absorbed by the cells in the body and produces a signal that can be detected by the scanner. This signal is used to create images of the inside of the body, showing any areas where cancer may have spread. The scan is usually completed in less than an hour, and results are typically available to the referring consultant within 24 hours.

Why PET/CT scans are used

A PET/CT scan is useful in revealing or evaluating several conditions, including many cancers, heart disease and brain disorders.

Blackrock Health uses the referral criteria, ‘iRefer Guidelines, Making the Best Use of Clinical Radiology’. These guidelines are considered when requesting a diagnostic radiology/nuclear medicine examination, and means that you receive the most useful test to diagnose your condition.

How PET/CT scans work

PET/CT scanners work by detecting the radiation given off by a substance, called a radiotracer or a radio-isotope. In particular, the scan tracks the presence of this substance as it passes through different parts of your body.

In most PET scans a radiotracer called fluorodeoxyglucose (FDG) is used. This is similar to naturally occurring glucose (a type of sugar) so your body treats it in a similar way.

By analysing the areas in which the radiotracer may or may not be active, it is possible to work out how well certain body functions are working and identify any abnormalities.

For example, a concentration of FDG in the body’s tissues can help identify cancerous cells. This is because cancer cells use glucose at a much faster rate than normal cells.

Is the radiation dangerous?

Exposure to large amounts of radiation can be harmful. However, there is no direct evidence that low exposures to radiation are harmful – but it is considered sensible to limit exposures to the lowest amount possible.

All staff involved in the medical exposure of patients are highly trained to ensure the radiation dose delivered as part of the scan is as low as reasonably achievable while ensuring we can get high quality diagnostic images.

It is the duty of Doctors who order scans, and Radiology staff who carry out the scans to ensure that the scans are justified. This means that staff must ensure that when scans are ordered, the benefits from making the right diagnosis and consequently giving you the right treatment outweigh any small risk involved.

If treatment decisions depend on findings, then the risk to your health from not having the scan is likely to be much greater than that from the scan itself.

Why are precautions advised after PET scans?

The injected radioactivity can remain in the patient’s body up to 8 hours after injection. It is generally excreted from the body via the kidneys and urine. For this reason certain aftercare and precautions are recommended for the patient and people who come into close contact with the patient ( i.e. people referred to as comforters and carers). The radiographer will inform you on the length of time precautions should be followed.

Preparing for a PET/CT scan

PET/CT scans are carried out on an outpatient basis. This means you won’t need to stay in hospital overnight.

It is important to arrive on time for your scan as the radiotracer used has a short shelf-life and your scan may be cancelled if you are late.

Your appointment letter will include all preparation needed before your appointment. You will be advised not to eat anything for 6 hours beforehand.

Drinking is allowed, however, you may only drink plain, unflavoured water. You should also avoid strenuous exercise for 24 hours before your appointment.

It is advised to wear loose, comfortable clothes. It may be possible to wear these during the scan, although you may be asked to change into a hospital gown.

Avoid wearing jewellery and clothes that have metal parts, such as zips, because these will need to be removed.

What happens during the scan

Radiotracer injection

Before the scan, the radiotracer is injected into a vein in your arm or hand. You will need to then rest quietly for about an hour, in an uptake room, to allow the radiotracer to be absorbed by the cells in your body.

It is important to relax, keep as still as possible, and to avoid talking or reading while you wait as these activities will affect the radiotracer uptake in the brain and have an impact on the resultant scan.

You will be asked to go to the toilet before having the scan, so there isn't a normal collection of the radiotracer in the bladder, which might obscure surrounding structures.

The scan

During the scan, you lie on a flat bed that’s moved into the centre of the large, cylindrical scanner.

You must stay still while the scan takes place.

The scan can take up to 30 minutes. Having the scan is completely painless, but you may feel uncomfortable lying still for this long.

The operating radiographer can see and hear you throughout your scan. If you feel unwell or need assistance at any point you can signal or call out to the radiographer and they will be with you immediately.

After the scan

You shouldn’t experience any side effects after having a PET scan and can go home soon afterwards.

The results of your scan will not be available on the same day, however they will be sent to your specialist within 48 hours of your scan.

Are there any risks?

The amount of radiation you receive is small and the risks are low, similar to that of other radiological tests.

The radiotracer you receive becomes less radioactive over time and will usually be passed out of your body naturally within a few hours. Drinking plenty of fluid after the scan can help flush it from your body.

As a precaution, you will be advised to avoid prolonged close contact with pregnant women, babies or young children for a few hours after having a PET scan as you will be slightly radioactive during this time.

Aftercare for patients:

Patients should drink plenty of fluids and empty their bladder frequently. When using the toilet they should avoid spills, flush twice and wash their hands thoroughly.

Nursing mothers should express and discard breast milk for the length of time the radiographer advises and ideally arrange for someone to look after the baby for the rest of the day.


Even though the amount of radiation that comforters and carers might potentially be exposed to is very low, the following precautions are recommended:

The patient should avoid close contact with pregnant women and young babies for 8 hours.

Comforters and carers should avoid direct continuous contact with the patient, particularly in the case of a child sitting on your lap watching television.

The patient shouldn’t undergo any non urgent investigations and treatments that would involve close staff contact with the patient for periods longer than 30 mins. Such treatments or examinations should be postponed for at least 6 hours post injection.

The patient should not undergo blood tests, urine samples and surgery. They should be postponed for 24 hours post injection. Clinical urgency, in some circumstances may allow for exceptions.

How do I get this?

PET CT  requires a Consultant referral letter before you make an appointment.

Is this insured?

Not all services are covered by health insurance. To find out if you're covered, please check your health insurance before your visit. You can do this on our health insurance cover check page, or by contacting your health insurer. 

How do I pay?

If you do not have health insurance or your health plan does not cover the full cost, you will need to pay the balance due before your treatment or procedure. You may be able to claim back some fees on your insurance. To pay an excess not covered by your insurance or any other inpatient fees, please visit our payment page. If you have any queries about paying for your care, please contact the finance team in your hospital.

Available at:
  • Blackrock Clinic
  • Galway Clinic
  • Hermitage Clinic

Blackrock Clinic

Rock Road, Blackrock, Co. Dublin, A94E4X7
PET /CT Scan

Galway Clinic

Doughiska Galway, Galway H91HHT0
PET /CT Scan

Hermitage Clinic

Old Lucan Road, Dublin, D20 W722
PET /CT Scan