Explanation

MRI stands for magnetic resonance imaging. It uses a big strong magnet and radio waves to take detailed pictures of your insides.

MRI can give doctors detailed pictures of nearly every part of your body, but they are usually used to help them to get a better look at your brain, pelvis, spinal cord and liver. MRI is also good for showing things like muscles, joints, bone marrow, blood vessels and nerves, and organs like your brain and heart.

It is better than having an X-ray because it gives more detail and can show things like swelling, inflammation and blood flow. The pictures taken by MRI are usually two-dimensional, but sometimes a three-dimensional image can be built up and shown on a computer screen.

Why do I need one?

You might need an MRI if you have a problem with your bones or joints. It can show injuries to, or abnormalities of, tendons, ligaments, muscles, cartilage and bone marrow and can help your doctor decide if an injury needs surgery.

Your doctors can see lots about how your brain works from an MRI because it can measure changes in blood flow. It can also tell them if your brain has been damaged by lack of oxygen if you have had a stroke.

MRI can also show your heart and the large blood vessels around it really well, so this helps with diagnosing heart problems.

If your doctors think you have a tumour, MRI is really good for helping them to see exactly where it is. It can also show them how deep a tumour has grown and also whether it has spread. After surgery, surgeons can even use MRI to make sure they have taken all of the tumour out.

How does it work?

Your body is made up of billions of tiny things called protons. These protons are so small, that they are even smaller than a grain of sand. An MRI works by taking pictures of your protons!

The protons sing, like a choir and the magnet conducts the choir! It tells the protons when to start singing. When they sing, they wobble, and the computer turns this singling and wobbling into a picture. WE can't hear the protons singing, but the computer can.

Different areas of your body are louder or quieter, depending on how many protons are singing. The more protons that are singing, the louder, the less that are singing, the quieter. The protons sing a different song and make a different picture for each illness or abnormality, so doctors can tell what the problem is and where in your body it is.

Do I need to do anything before I have it?

You will probably be able to eat and drink as normal. If you are having an MRI of your lower body though (like your stomach or pelvis), your doctor may tell you not to eat or drink for about 5 hours beforehand. On the other hand, your doctor might ask you to drink lots of water before the MRI. They will likely do this if they think you have Crohn's disease for example.

You might have an injection of a special dye that helps to make the picture clearer. Don't worry though, you can have a special cream or spray to make your skin go numb so that you won't feel a thing!

You must remove any metal items that you are wearing or have on you. This includes things like watches, jewellery, hair clips, keys, coins and mobile phones. You should also make sure you don't wear any clothes that have metal zips, fasteners, buttons, belts or buckles. Make sure your doctor knows if you have an artificial limb or joint, a pacemaker, or screws or plates inside your body from surgery you have had before. This is very important because the magnet used by MRI is VERY strong and powerful, so if it comes into contact with any metal, it can attract it, which could be dangerous. Also, the pictures taken may not come out properly.

What happens?

You lie on a bed in a machine called an MRI scanner. It's like a short tunnel, which is open at both ends. The bed is motorised and it passes through the scanner. It usually only takes 15-20 minutes to have an MRI, but it can take up to an hour.

You have to lie completely still during this time, for up to 3-5 minutes at a time, to make sure that the pictures don't come out blurry. If you think you will find it hard to stay still, the doctor can give you some medicine that will make you feel sleepy.

The MRI scanners can be very noisy, due to the magnet being switched on and off. You will be given headphones to block out the noise though, and you will probably be able to listen to music.

The radiographer (an expert in producing MRI pictures) uses a computer to operate the MRI scanner. The computer has to be kept away from the magnet, so it is in a separate room from the one in which you are having the MRI. This means that the radiographer will also be in this room, but you will be able to talk to him or her using an intercom, and he or she will be able to see you all the time on a monitor.

While you have your MRI, your Mum or Dad can stay in the room with you, so you won't ever be alone.

When the MRI is finished, you will come back out of the scanner.

Will it hurt?

No. MRI is totally painless. It's important to be as comfortable as possible while you are having it though, because you must keep the part of your body being photographed very still to make sure the pictures don't get blurred.

What happens next?

You usually have MRI as an outpatient, so that means you won't have to stay in hospital overnight. When it has finished, you will probably be able to go back to doing everything you normally do straight away. If you have had medicine to make you sleepy though, you will have to relax and take it easy for a day or so when you get home - so no riding your bike or going roller blading!

If you have had an injection of special dye to make the picture clearer, it's a good idea to drink lots of water for the next day or so to help get the liquid out of your body.

A radiologist (a doctor who is an expert in MRI), will need to have a look at the pictures, and will send a report to your doctor so that he or she can talk about the results with you. This usually takes a couple of weeks unless the results are needed urgently.