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Your questions about MRI scans answered

MRI scanning creates an image of the inside of your body to help doctors diagnose conditions and plan treatments – but how does it work and what is involved?

MRI (magnetic resonance imaging) scanning can give your doctor a comprehensive picture of what is going on inside your body. This is useful for working out what may be wrong with you if you are experiencing particular symptoms, and deciding which treatment will be the most effective.

What does an MRI scan show?

An MRI scan is often the first step in diagnosing neurological conditions, heart disorders and orthopaedic issues. If you have already had treatment for a diagnosed condition, an MRI scan can also show how effective this has been.

How do MRI scans work?

An MRI scanner uses strong magnets and radio waves and can examine almost any part of your body to produce a detailed cross-section image. MRI scanning is often used to look at areas such as the brain, breasts and internal organs, and can also give an accurate picture of bones, joints, blood vessels and your spinal cord.

Each of the atoms in your body is highly sensitive to magnetic force. The strong magnets in an MRI scanner make all the atoms in your body line up in the same direction. The scanner then sends short bursts of radio waves to knock the atoms out of alignment, before the magnet pulls them back into line again. As the atoms realign themselves they send out a radio signal, showing exactly where they are in your body.

In an MRI scan the atoms in your body behave like the pixels on a computer screen. There are millions of atoms sending millions of signals, and the atoms of each type of tissue in your body produce a different signal. These signals show up as the different elements of a detailed image.

What happens during an MRI scan?

An MRI scan usually takes between 15 and 90 minutes, depending on how much of your body is being scanned. You will lie on a flat bed, which slides into the tube-shaped MRI scanner. You may go into the scanner head first or feet first, depending on which part of your body is being scanned.

It’s very important to keep as still as you can while the scanner is working so that the image is as accurate as possible. You will be given headphones or earplugs to wear, as the MRI scanner makes occasional loud tapping noises when the electric current switches on and off.

Your MRI scan will be carried out by a highly trained radiographer, who controls the scanner from another room using a computer. They will be able to see you on a TV monitor to keep an eye on you throughout the scan, and you’ll be able to speak to them from the scanner via an intercom.

Are MRI scans safe?

MRI scanning is one of the safest imaging techniques there is. It is also painless, although if you have claustrophobia you may find going into the scanner slightly uncomfortable. The radiographer will be accustomed to helping people deal with claustrophobia and can support you throughout the scan.

The reason MRI scanning is so safe is that it does not use X-rays, meaning you are not exposed to any potentially harmful radiation. Some people are particularly vulnerable to the effects of radiation, such as pregnant women and babies, and these people are often recommended for MRI scanning.
There has been a great deal of research into whether there is any risk to the human body from the magnetic fields and radio waves used for MRI scanning. There is no evidence to suggest that there is any risk at all to your body and MRI scanning is actually one of the safest medical procedures available.

MRI scanning is suitable for the vast majority of people, but if you have certain implants fitted, an MRI scan may not be safe for you. This includes pacemakers, which are battery-operated devices helping to control an irregular heartbeat.

You can opt to have your MRI scan at a BMI Healthcare hospital and the procedure is covered by most medical insurance policies.

If you want to learn more about what it's like to get an MRI scan, read about our patient's experience with MRI scanning.

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