About MRI's
An MRI scanner takes images of the body, using a very powerful magnetic field and radio waves.
The scanner is a large, tube‑shaped machine. It has a large hole through the middle and is open at both ends. You lie on a narrow bed that moves slowly into the scanner while detailed images are taken.
Preparing for an MRI scan
Your appointment letter will tell you exactly what you need to do before your scan, read it carefully before you arrive.
Visit About the Radiology Department for more information about:
- what to expect at your appointment
- changing or cancelling an appointment
- accessibility and language support
- bringing someone with you
- possible appointment fees
MRI safety checks
MRI scanners use a powerful magnetic field, which can move some medical implants or affect how they work. This means an MRI scan is not safe for everyone.
Before entering the MRI scanning area, you must complete a safety questionnaire. This helps us check that an MRI scan is safe for you.
You must tell us if you:
- are, or think you might be pregnant
- have ever had metal fragments lodged in your eyes or elsewhere in your body
- have any of the following:
- an implanted defibrillator or pacemaker
- a cochlear (ear) implant
- artificial heart valves
- implanted drug infusion ports
- artificial limbs or metallic joints
- implanted nerve stimulators
- metal implants, such as pins, screws, plates, stents or surgical clip including aneurysm clips
Additional checks
In some cases, you may need an X‑ray before your MRI scan to confirm it is safe for you to enter the scanner.
If you are unsure about any item on the questionnaire, speak to the radiographer.
What to expect during an MRI scan
When you arrive, we’ll give you a hospital gown and trousers to wear. We’ll help you get comfortable on the scanner bed before the scan begins.
The scanner can be very noisy, so we’ll give you headphones to protect your ears. We can also play music or the radio through the headphones if you’d like.
The radiographer, carrying out your scan, can see you at all times and can talk to you throughout the examination.
Injections during the scan
You may be given one or more injections during your MRI scan, including:
- MRI contrast, this helps produce clearer and more detailed images
- Buscopan, this helps relax your abdomen so it stays still and clear images can be taken
If Buscopan is needed, we’ll send you the manufacturer’s information leaflet before your appointment.
How long an MRI scan takes
Scanning an area of the body usually takes between 30 minutes to 1 hour.
Allow up to 2 hours for your appointment, as urgent or emergency cases may occasionally cause delays. If this happens, we’ll keep you informed.
The video guidance for MRI patients at the General Hospital on YouTube explains what to expect when you arrive and what will happen at your appointment.
MRI scan with contrast
Sometimes we may give you an injection of a fluid called contrast. This helps improve the quality of the images.
Read all the information in your appointment letter and booklet carefully before you arrive.
The contrast is usually injected into a vein in your arm. The person giving the injection will explain what they are doing and check that you are happy to proceed.
After an MRI scan with contrast
After the examination:
- stay in the department for 30 minutes
- drink plenty of water for the next 24 hours to help the flush the contrast from your system
The contrast will leave your body naturally when you pass urine. You won't notice anything different.
Possible side effects of MRI contrast
MRI contrast is generally very safe and serious side effects are rare.
There is a very small risk of an allergic reaction.
Tell a member of staff straight away if you experience:
- wheezing or difficulty breathing
- a rash or itching
- swelling of the face, lips, tongue or throat
If you experience any of these symptoms while you're in the department, tell a member of staff immediately.
If you experience any of these symptoms after you leave your appointment call the MRI Department Immediately.
Out of hours, contact the Emergency Department by calling +44 (0) 1534 442246.
Getting your results
The doctor or healthcare professional who referred you for the MRI scan will usually receive the results within one week.
Occasionally, it can take longer. If this is the case, we'll tell you after your scan.
How an MRI scan works
Your body contains millions of hydrogen atoms. These atoms contain particles called protons which normally point in different directions.
Inside the MRI scanner:
- the powerful magnetic field causes the protons to line up
- short bursts of radio waves temporarily knock the protons out of position
- the radio waves stop, the protons return to their original position and release radio signals
Protons in different types of body tissue return to their original position at different speeds and the signals they release vary.
A detector placed behind, or around, the part of the body being scanned picks up these signals and sends them to a computer.
The computer uses this information to create detailed images of the inside of the body.
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