A young person's guide to
Magnetic Resonance Imaging (MRI) is one of the main technologies we use to look inside our bodies. It's an excellent way to diagnose multiple sclerosis, brain tumors, torn ligaments, tendonitis, cancer and strokes, and many others.
Imaging specialist Dr Erik O'Hanlon explains how an MRI machine works.
The heart of an MRI is basically just a strong magnet and a radio transmitter and receiver, plus a lot of electronics to coordinate their operation.
An MRI scanner contains large magnetic coils made from superconducting magnets
So when you enter an MRI machine, it's like entering the field of a gigantic magnet
To simplify our explanations, we're going to represent the MRI scanner as a gigantic magnet
Your body enters the magnetic field of the MRI scanner
Hydrogen protons in your body line up with the magnetic field
Radiofrequency pulse excites hydrogen atoms
Then turn off the radiofrequency pulse. Protons are left with all this extra energy
MRI Scanner detects the energy released by the protons
By measuring the time taken to release energy, the type of tissue can be determined and a picture generated
Is that all there is to it?
Well, that's the quick version. As Erik says, the full physics behind MRI imaging is a bit more complex. For a more detailed explanation listen to another neuroscientist in the Guardian's Science Weekly.
Why would you get an MRI scan and how is it different from other scans like X-rays?
You may be familiar with other ways of creating images of our bodies like X-rays which are great at showing bones. An MRI is excellent at showing details of soft tissues in our body such as muscles, ligaments, organs and so on.
X-Ray vs MRI
Compare the images of a human head shown here. The left is an MRI and the right is an X-ray.
What are the main differences that you can see?
Can you think of a situation where doctors might prefer one scan over the other?
Brain diseases that MRI can detect
Some of the brain diseases that an MRI scan can detect are:
Look through the MRI images to see what these diseases look like on a scan.
One of the simple things to look for is a lack of symmetry.
Time to be a scientist. Would you like to have a go at analysing a real MRI scan?
Erik has been kind enough to lend us his brain for this. Literally! This scan is a collection of horizontal images of Erik's brain. Watch the movie and see what you can identify, it might take a few goes to makes sense of it.
While the full anatomy of the head is pretty complicated, start by looking for the simpler things like teeth, eyes and his nose. That will help make sense of it all.
Is an MRI scan safe?
Yes, provided you don't have an implant like a pacemaker that would be affected by the magnet. There is no ionizing radiation that you would experience in an X-ray so MRI scans are much safer. A more detailed list of things to look for can be found here.
What does an MRI machine sound like?
Surprisingly loud! The noise can be up to 110 decibels which is about as loud as a live concert. I won't lie, it's not the most pleasant sound so we usually use earplugs so the patient isn't put off by it.
Where does the noise come from?
A second magnetic field is created using gradient coils to help determine where the protons that we're looking at are. This is switched on and off rapidly. Since it's so strong, the coils try to move with a lot of force and this creates the noise.
How long does it take?
Depending on the type of scan, it will take from 15-90 minutes.
An MRI machine is basically a giant magnet. The one in Trinity College Dublin is a 3 Tesla machine - that's about 60,000 times stronger than the earth's magnetic field.
Despite a lot of safety protocols, accidents can happen especially when people who aren't familiar with MRI scanners are working in the area.
History of MRI
A detailed history
Who really invented MRI?
The first MRI scanner
More detail on how MRI works
How it Works
Why it is so noisy
Contributions to Medical Science
Why the Nobel prize was awarded for the invention of MRI scanning
Irish athlete Thomas Barr talks about MRI scans for sports injuries