What an MRI scan is
An MRI scanner takes images of the body, using a very powerful magnetic field and radio waves. The scanner has a large hole through the middle and is open at both ends.
Preparing for your appointment
Follow the instructions on your appointment letter. It might give you instructions about eating and drinking and having a blood test. It's very important you fill in the Safety Questionnaire and bring it with you on the day of your scan.
Metal items can't be taken into the scanning room. You will need to remove jewellery, particularly body piercings. It's not usually necessary to remove wedding rings. Lockers are provided, but it's preferable for you to leave valuables, such as jewellery at home.
We recommend that you don't wear eye make-up as this can affect the quality of some scans. All medication can be taken as normal.
We cannot look after your children during your scan. Patients under the age of 16 who are being scanned, must be accompanied by an adult.
What you should tell us
The MRI scanner uses an extremely strong magnet, so we cannot scan people with certain types of medical implant. This is because the magnet could move the implant or affect its function.
Before you enter the scanning area you will have to fill in a questionnaire so that we can make sure an MRI is safe for you.
Tell us if:
- you are, or could be, pregnant
- you have ever had metal fragments lodged in your eyes or your body
You also need to tell us if you have any of the following medical devices in your body:
- internal (implanted) defibrillator or pacemaker
- cochlear (ear) implant
- artificial heart valves
- implanted drug infusion ports
- artificial limbs or metallic joints
- implanted nerve stimulators
- pins, screws, plates, stents or surgical clips such as for aneurysms
In some cases you may need an x-ray before an MRI scan to make sure you are safe to enter the scanner.
What to expect during your scan
When you arrive, we give you a hospital gown and trousers to put on. We make you as comfortable as possible on the scanner couch. It's very noisy so we give you headphones to protect your ears. We can play music or the radio through the headphones. The Radiographer doing the scan is able to see you and talk to you during the scan.
As part of this examination, it's likely we will give you an injection of MRI contrast. We will also give you an injection to help relax your abdomen (Buscopan). This helps to keep it still so we can get clear pictures. If you need to have this, we will have sent you the drug information leaflet supplied by the company who make the drug.
How long it takes
Scanning one area of the body takes about 30 minutes but it can take up to an hour. Allow up to 2 hours for your appointment as we sometimes have to fit in emergency cases and unexpected delays can occur. If this happens we'll keep you informed.
MRI scan with contrast
Sometimes we need to give you an injection of a special fluid we call a contrast agent. It's important that you read all of your appointment letter and booklet to prepare for this examination.
During the examination, the MRI contrast is usually injected into a vein in the arm. The person going to do the injection will explain what they are going to do and check you are happy for them to carry on.
After the injection, we ask you to stay in the department for 30 minutes. It's important to drink plenty of water for the next 24 hours. This helps to remove the fluid we have injected from your body. It will come out when you go to the toilet to pass water but you won't notice anything different.
Risks and complications of MRI contrast
MRI contrast does not normally have any serious side effects. There is a very small risk that you might suffer from an allergic reaction. This can cause wheezing or difficulty in breathing, a rash, itching, or swelling of the face, lips, tongue or throat. If you get any of these symptoms, you must tell us straight away.
If any of these symptoms develop after you have left the MRI Department, contact us on +44 (0) 1534 442861. After 5pm and at weekends, call Emergency Department +44 (0) 1534 442246.
Getting your results
The doctor that sent you for the MRI scan will get the results in approximately 1 week. Sometimes it's a little longer and if this is the case, we will tell you after the scan.
How an MRI scan works
Your body contains millions of hydrogen atoms which contain particles called protons. When you are in an MRI scanner all the protons line up in parallel to the strong magnetic field, like tiny magnets. Normally the millions of protons all lie in random directions. Then, short bursts of radio waves are sent from the scanner into your body. These radio waves knock the protons from their positions. When the burst of radio waves stops, the protons line up back into place and emit radio signals.
The protons in different tissues of the body line up at different speeds. So, the signal emitted from different body tissues varies. For example, softer tissues can be distinguished from harder tissues on the basis of the signals sent. These signals are detected by a receiving device in the scanner.
A detector is placed behind, or around, the part of the body being examined and detects these tiny radio signals and transmits them to a computer. The computer creates a picture based on the radio signals emitted from the body. You should not have any after-effects from the scan.