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What is an MRI scan?

MRI stands for Magnetic Resonance Imaging. An MRI scan uses magnetism and radio waves to build up a picture of the inside of the body. It can show how deeply a tumour has grown into body tissues. For some types of cancer it can tell whether the tissue left behind after treatment is cancer or not.

The scanner is a large machine with a doughnut shaped hole. You can’t feel anything when you are having the scan but the scanner is very noisy.

Having an MRI scan

Your doctor will tell you if you need to do anything beforehand, such as not eating. For some scans, you have an injection of a dye called contrast medium that shows up body tissues more clearly. You need to remove any metal objects such as jewellery and belts, and need to empty your pockets. You can’t have an MRI if you have any metal inside your body, such as surgical clips, metal pins or plates, or a pacemaker.

You lie on a narrow couch which moves through the scanner. The radiographer controls the scan from outside the room. They can see you and talk to you. You need to lie still and you wear earphones because the scanner is very noisy.

MRI scans can take up to an hour and a half. Contact the department before your test if you are likely to feel claustrophobic. The staff can arrange to give you medicine to help you relax.

MRI scans are very safe. Rarely, people have an allergic reaction to the contrast medium and the staff give medicines to control the reaction.


It usually takes a couple of weeks to get the results. Contact your doctor if you have not heard anything by this time.


CR PDF Icon You can view and print the quick guide for this page about MRI scans.



What an MRI scan is

MRI stands for Magnetic Resonance Imaging. This type of scan uses magnetism to build up a picture of the inside of the body. Below is an example of an MRI scan of the head.

MRI scan

MRI is completely painless, but the scanner is very noisy. The MRI scanner creates cross section pictures of the body. It can show up soft tissues very clearly and a single scan can produce many pictures from angles all round the body. The pictures can be affected by movement so they aren't used very often for some tumours because coughing, swallowing or breathing will make the scan less clear.

MRI can be used on most areas of the body. For some parts of the body and for some types of tissues, it can produce clearer results than a CT scan. For other situations, the CT scan is better. Your own doctor will know which is the best type of scan for you.

MRI is particularly good for some types of brain tumour, primary bone tumours, soft tissue sarcomas and for tumours affecting the spinal cord. In some situations, your doctor may suggest MRI if a CT scan hasn't been able to give all the information they need. In some early cancers, such as cervix or bladder cancer, MRI is better than CT at showing how deeply the tumour has grown into body tissues. It can be particularly useful for showing whether the tissue left behind after treatment is cancer or not.

As well as being used to find or stage tumours, MRI can be used to measure blood flow. You may have an injection of a special dye before the scan to help make the pictures clearer.


The photo above shows an MRI scanner. It is a large cylinder with a couch that can move backwards and forwards through the cylinder. The pictures are taken inside the cylinder. The MRI is in a protected room to keep out radio waves as these interfere with the scan.


Preparation for the scan

Some MRI scans need preparation beforehand. If there are special preparations, you will be told about them in plenty of time. You can take all your medicines as normal beforehand. You may be asked not to eat for at least an hour before your scan. Some stick on patches for medicines (transdermal patches) may cause burns if they contain metals because the MRI scan can make the patches overheat. So let the MRI staff know beforehand if you normally use patches for medicines. The staff can work out how you can safely take off the patches before the scan if necessary.


Having an MRI scan

View a transcript of the video showing what happens when you have an MRI scan. (Opens in a new window)

Once you have checked in at the scan department, the receptionist will ask you to take a seat in the waiting room until the radiographer or helper calls you. At this point, you will have to complete and sign a checklist for safety. The checklist asks you about any medical conditions you may have or operations you have had, mainly those that may involve any metal implants. This includes pacemakers, surgical clips, pins or plates and cochlear implants (for deafness).

If you have your ears (or any other part of your body) pierced, you will have to take out your rings or studs before your scan. If you have a contraceptive coil (IUD) fitted, you must tell the radiographer as some have copper wire in them. You should also tell them if you think you may have any metal fragments anywhere in your body - this sounds odd but is common in people who do metalwork or welding for a living. If you think this is possible in your case, you'll need an X-ray before the MRI to check.

When it is time for your scan, you may first go to a cubicle to take off your outer clothing down to your underwear and put on a hospital gown. Don't forget to remove jewellery, watch and hair clips. If you are just having an MRI of your head, you may not have to undress.

The scan uses a very powerful magnet. If you still have your clothes on, it is best to empty your pockets. You need to remove all coins, keys and credit cards so it might be easier to take everything out. Because there is no radiation, it is safe to take a relative or friend into the scanning room with you if you like. They will also have to take off everything metal. Remember little things like hair slides, cufflinks and belt buckles.

When you are ready, the radiographer will take you into the scanning room. You will need to lie down on the MRI couch. Most MRI scans are done with you lying on your back. You have to lie as still as you can, but breathe normally. Your radiographer will explain any instructions beforehand. You may have to hold your breath at points during the scan so that you move as little as possible. Any movement can blur the scan.

The radiographer may offer you ear plugs or headphones to wear. MRI scans are very noisy. The noise is like a loud clanging inside the cylinder and it goes on throughout the scan. The radiographers prefer that you wear some sort of ear protection to protect your hearing and for your own comfort. And you may be able to listen to music while the scan is going on.

Once you are positioned in the scanner, the radiographer will go out to the control panel. They will be able to see the scanning room through a window or on a TV screen and you can talk to each other through an intercom. They will tell you that they are about to start the scan and remind you to keep as still as you can.

When the scan is over, the radiographer will come back into the room and help you down from the couch.

An MRI scan can take anything from half an hour to an hour and a half. Lying still for that long can be uncomfortable. If you are getting stiff and need to move, tell the radiographers through the intercom. It is very important to keep as still as you can, otherwise parts of the scan may have to be done again and may take longer. You should be able to go home as soon as the scan is over.

Some people feel a bit claustrophobic (closed in) when they are having a scan. If you think you are likely to feel this way, tell the radiographers before the day of your scan. If necessary, you can have a tablet or injection to calm you. If you need a sedative, it needs to be organised in advance so if you think you'll need one, do ring the department as soon as your appointment comes through. If your radiographers know that you are nervous, they will take extra care in making sure you are comfortable and understand what is going on. Keeping your eyes closed sometimes helps. And in some centres it may be possible for you to take in some favourite music that the radiographers can play through your headphones to help pass the time.


Injections before the scan

You may have an injection of a dye (called contrast medium) just before the scan. This helps to make the scan clearer. This is particularly likely if you are having a whole body scan as the dye makes the body organs show up more clearly.


Is MRI safe?

MRI is very safe because of the checklist you fill in beforehand. There are some people who cannot have an MRI but the checklist will make sure this is picked up. The scan uses magnetism, so metal will affect it. If you have certain types of metal surgical clips, metal pins or plates or a pacemaker inside your body, you cannot have an MRI scan.

Very, very rarely, someone has an allergic reaction to the contrast medium injection. The reaction most often starts with sweating, rash and difficulty breathing. The doctors and radiographers will know what to do if you have this type of reaction.

Generally you won't be given an MRI scan if you are pregnant, but it can be done if absolutely necessary.


The results

It can take time for test results to come through. How long will depend on why you are having the scan. Usually, a specialist in MRI sees the scan and dictates a report to be typed up. The report is then sent to your specialist, who gives the results to you. If your GP has sent you for the test, the results will be sent directly to the GP surgery.

Understandably, waiting for results can make you anxious. It usually takes a couple of weeks for the results to come through. If your doctor needed the results urgently, it would have been noted on the scan request form and the results will be ready sooner than that. Try to remember to ask your doctor how long you should expect to wait for the results when you are first asked to go for the test. If it is not an emergency, and you have not heard a couple of weeks after your test, ring your doctor's secretary to check if they are back.

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Updated: 13 August 2013