PET-MR Scanning: Frequently Asked Questions

What is a PET-MR scan?

PET-MR is a new type of scan in which a PET scan and an MRI scan are performed at the same time.

PET stands for Positron Emission Tomography. This is a scan that requires the injection of a small amount of radioactivity, most commonly a tiny amount of radioactive sugar, which travels around the body and is taken up by parts of the body that use a lot of sugar. Using the PET scanner we can see the increased use of sugar and then can localise the exact part of the body using the MRI scan.

MRI stands for Magnetic Resonance Imaging. An MRI scan uses a combination of a strong magnet and radiowaves to produce detailed pictures of the inside of your body.

The combination of the two scans provides added information for your doctor related to the medical problem you have.

What are the benefits of a PET scan?

A PET scan is a very sensitive and accurate method of detecting changes in metabolism associated with diseases, often before abnormalities show up on ordinary scans. A drawback is that it is less good at showing the exact anatomy of where the abnormality is; this is why there is benefit from combining a PET scan and an MRI scan.

What are the benefits of an MRI scan?

An MRI scan can help to find out what is causing your problem and help your doctor to find the best treatment for you. An MRI scan provides much more detailed pictures of your body than an ordinary X-ray. It is particularly good at identifying problems in the spine, the brain, the heart and in the joints. It is also helpful for looking at other parts of the body, often when other types of scan have not given a full picture. Unlike X-rays and CT (Computed Tomography) scans, MRI scans do not use radiation.

When combined with a PET scan, both types of information can be used together to improve the diagnosis from one scan alone.

Are there any risks?

The PET scan does involve radiation. Any amount of radiation has a small risk but the level of risk versus the benefit that may be gained from having the scan is considered very small.

MRI is a very safe procedure for most patients. However, patients with heart pacemakers and certain other surgical implants, for example a cochlear implant, cannot be scanned.

You will be asked to complete and sign a safety questionnaire before your scan to make sure it is safe for you to be scanned.

Is it safe for me to have a PET-MR if I am pregnant?

We do not usually carry out PET scans on pregnant patients since this would give a radiation dose to your unborn child, which we want to avoid. If you discover you are pregnant after a scan then we can discuss any possible issues with you. If you are breast feeding we may need to give special instructions to you.

Are there any alternatives?

If you cannot have a scan, for example if you have a pacemaker, the doctor may suggest an alternative type of imaging. This could be a PET-CT scan, a CT scan or an ultrasound scan.

What will happen to me during the scan?

This will depend on the type of scan, and will be fully explained to you by our staff when you arrive. A small needle will be inserted into a vein in your arm, hand or foot and the tracer injected. If you are having a brain or body scan you will be asked to relax quietly for between 30-90 minutes. Heart studies usually begin immediately. You will then be moved to the scanning room where you will be asked to lie very still on the scanning couch for as long as the scan takes. You will be given some breathing instructions for the CT part of the scan. This is done at the beginning of the procedure; after this you can just relax.

Do I need to confirm my appointment?

Yes, it is very important that you telephone to confirm your appointment so that we can give your time to another patient if you are unable to attend. Failure to do so could result in your appointment being cancelled. It is also important that you allow plenty of time to get to the PET Centre for your appointment, as scans generally cannot be delayed. You must tell us in advance if you know you are (or think that you may be) pregnant, are breast feeding or are the primary carer of small children. We may need to give you additional information.

We also need to know if you are diabetic or have any problems with your kidneys.

Giving your consent (permission)

The radiographer/technologist (member of the imaging team trained to carry out scans) will ask you if you are happy for the scan to go ahead. This is called verbal consent and may only involve checking you are booked for the correct scan. If you do not wish to have the scan or are undecided, please tell the radiographer/technologist.

It is your decision and you can change your mind at any time. Please bear in mind that not having the scan may delay your diagnosis as the doctors may not have all of the information that they need. Please remember that you can ask any questions you have at any time before, during or after your scan. If you would like to read our consent policy, please tell a member of staff.

What do I have to do to prepare for the scan?

We will need you to fast (NO food and NO drinks containing sugar or milk) and only drink water for 6 hours prior to most scans. In some circumstances this will be changed but we will inform you of this for specific scans. If you are diabetic, we will give you specific instructions about your medication and will book your scan at the best time to help adjust medication.

Will I need an injection?

The PET part of the scan requires an injection of the radioactive tracer. This is given into a vein by a small plastic tube, a cannula, in your vein. We will also check the level of sugar in your blood at the same time. You will then be asked to lie down on a couch for up to 90 minutes depending on the type of scan. You will then be taken into the scanning room.

As part of the MRI scan, if we are scanning certain areas of your body, we may need to give you a further injection of contrast/dye. This shows up on the scan and gives us more detailed pictures, particularly of your blood vessels. The injection will be given using the same small needle placed into the vein in your arm or hand. The contrast/dye contains gadolinium, which may, occasionally, cause allergic reactions. We do not give the contrast to people with poor kidney function or if you have had previous allergy to the dye. The most common allergic reactions can present as headaches, nausea and vomiting, sneezing, wheezing, runny nose, eye irritation, itching, hives, skin rash, swelling of the face, mouth, hands, feet or throat, difficulty in breathing, and low blood pressure.

Before your scan we will check whether you have had any previous allergies. If you would like more information about the injection, please ask the radiographer/technologist before your scan.

What do I need to wear?

We suggest that you wear something loose and comfortable. We may ask you to change into a hospital gown if any metal fastenings, such as zips or hooks and eyes, on your clothes are close to the area we are going to scan. This is because the fastenings may spoil the pictures.

You will need to empty your pockets of any coins, as these may be pulled out by the magnet and fly into the scanner. You will need to take off your watch and take any credit cards or travel cards with magnetic strips out of your pockets. The scanner can affect these and stop them from working.

If we are scanning your head, you will need to remove dentures which contain metal. Dental fillings will not affect the scan. Hairclips and wigs must also be removed if they contain metal.

What happens during the scan?

Before the scan, you will be given the opportunity to ask the radiographer/technologist any questions you have. We will take a short medical history from you and make sure you understand why you are having the scan and what the scan involves. A needle will be put into your hand or arm and then you will be taken to lie down on a couch where the radioactive injection will be given. You will then lie quietly on the couch for up to 90 minutes and then be taken to the scanner.

We will ask you to lie on the scanner bed where you will be made as comfortable as possible. If you are not comfortable, please tell us, as you will need to keep very still during the scan. It is important that you do not move, or the pictures could be blurred and the scan will have to be repeated. Once you are positioned correctly, we will move you into the scanner - the part of your body that we are scanning must be in the centre of the machine. For scans of the chest or abdomen, you may be asked to hold your breath for a short while.

When the scanner is working, it makes a loud banging noise. We will give you headphones to wear to reduce the noise. If we are not scanning your brain you can listen to music while you are being scanned so please bring in a CD of your choice! You will also be given a buzzer to press if you need to attract our attention during your scan.

How long will the scan take?

This depends on which part of your body is being scanned and the information that your doctor needs. The radiographer will tell you how long he/she expects your scan to take. Scans can take between 30 to 90 minutes depending on what types of images are required.

Will I feel anything?

The scan should be completely painless. The most difficult part is keeping still. Make sure you are as comfortable as possible before we start and try to relax. The scanner is a short tunnel, so if you get claustrophobia (fear of enclosed spaces) please let us know before you come for your scan.

Will there be anyone with me during the scan?

The radiographer/technologist will talk to you during the scan to let you know what is happening. If you are particularly anxious, a friend or relative can stay in the room during the scan.

Can I bring my children?

Unfortunately, because you are radioactive we advise that no children are brought to the scanning department since you will be with us for approximately 2-3 hours and your children would not be able to be with you.

What happens after the scan?

As soon as the scan is finished, you can go home, or back to your ward if you are staying in the hospital. You can eat and drink as normal and resume your usual activities. We normally supply a sandwich to eat after the scan.

The pictures taken during the scan are carefully studied by the imaging doctor who will produce a detailed report.

If you had the injection of contrast dye (not the radioactive tracer), an allergic reaction can very rarely occur up to two days after the scan (please read the Will I need an injection? section above for allergic reactions to look out for). If this happens, please contact the PET centre where you had your scan for advice. Alternatively, if it is out of hours, contact your local Accident and Emergency (A&E) department.

When will I get the results?

The results will be sent to the doctor who referred you for the scan. If you make a clinic appointment for two weeks after the scan, the results should be available. For more urgent problems, they will be available sooner.