An MRI scanner is a short cylinder that's open at both ends. You'll lie on a flat motorised bed that moves inside the scanner.
In some cases, a frame may be placed over the body part being scanned, like the head or chest. This frame contains receivers that pick up the signals sent out by your body during the scan. This can help to create a better quality image.
Depending on the part of your body being scanned, you'll be moved into the scanner either head or feet first.
Who operates an MRI scanner?
The MRI scanner is normally operated by a Radiographer, who is trained in carrying out imaging investigations. They control the scanner using a computer. This is in a different room to keep it away from the magnetic field generated by the scanner.
You'll be able to talk to the Radiographer through an intercom. They'll also be able to see you throughout the scan via a television monitor and a viewing window.
During the scan
At certain times during the scan, the scanner will make loud tapping noises. This is the electric current in the scanner coils being turned on and off. It can be extremely loud and patients have often compared it to standing immediately next to roadworks.
You'll be given earplugs or headphones to wear to help you feel more comfortable.
You're usually able to listen to music through headphones during the scan if you want to, and in some cases you can bring your own CD.
To avoid the images being blurred, it's very important to keep your whole body still throughout the entire scan.
Modern MRI scanners have a wider tunnel, which helps reduce claustrophobia. If you're claustrophobic you should tell the Radiographer. They'll be able to support you during your scan. Going into the scanner feet first may be easier for claustrophobic patients, although this isn't always possible.
How long does an MRI scan take?
A single scan may take a few seconds or 3 to 8 minutes. You may be asked to hold your breath during short scans.
The total scan lasts 15 to 90 minutes, depending on the size of the area being scanned and how many images are needed.
You'll be moved out of the scanner when your scan is over.
After the scan
An MRI scan is usually carried out as an outpatient procedure. This means you won't need to stay in hospital overnight.
After the scan, you can resume normal activities immediately. If you have had a sedative, a friend or relative will need to take you home and stay with you for the first 24 hours.
It's not safe to drive, operate heavy machinery or drink alcohol for 24 hours after having a sedative.
Getting your MRI scan results
Your MRI scan needs to be studied by a Radiologist (a doctor trained in interpreting scans and X-rays). It may also need to be discussed with other specialists. This means it's unlikely you'll get the results of your scan immediately.
The Radiologist will send a report to the doctor who arranged the scan. They'll discuss the results with you.
It usually takes 1 to 2 weeks for the results of an MRI scan to come through, unless they're needed urgently.
How does an MRI scan work?
Most of the human body is made up of water molecules. These consist of hydrogen and oxygen atoms.
At the centre of each hydrogen atom is an even smaller particle called a proton. Protons are like tiny magnets and are very sensitive to magnetic fields.
The MRI scanner has powerful magnets. This means that when you lie inside it, the protons in your body line up in the same direction. This is similar to when a magnet pulls the needle of a compass. You will not be able to feel this happening.
Short bursts of radio waves are then sent into the body, knocking the protons out of alignment. When the radio waves are turned off, the protons realign. This sends out radio signals, which are picked up by receivers.
These signals provide information about the exact location of the protons in the body. They also help to show the difference between types of tissue in the body. This is because the protons in different types of tissue realign at different speeds and produce distinct signals.