MRI. That fancy acronym doctors use, fewer people understand, and even fewer people actually explain. Until recently, I was one of those middle people, not fully understanding what exactly an MRI machine did. Now, thanks to University of Glasgow, I’ve been enlightened.
I honestly wish neuroscience was more accessible to everyone; I think it’s why I like writing little articles like these. I’ll start with some of the basics of MRI and provide nuggets of details. You can shout at me if you want to hear more detail about something specific – I love questions and thus they are encouraged!
So, what in tarnation is going on in a such a massive machine that makes all of these ridiculous sounds that sound similar to a construction site (or dubstep music)? Just view the 45 second video to see what I mean:
We’re gonna find out together.
What is MRI?
MRI = Magnetic Resonance Imaging, and the machine is basically an extremely fancy camera used to take a 3D image of the body, giving a unique look at what the insides look like. MRI can be used to study any body part – but of course, I’m going to focus on how it’s used on the brain. On a most basic level, the MRI machine takes many photographs at different depths (think of it as an invisible piece of paper slicing through you bit by bit) and then combines those images to show a full 3D picture of what’s going on in someone’s brain or other body part. See the below short video showing a sagittal (sagittal = fancy word for “side / profile view”) MRI scan of someone’s brain, uploaded by an awesome person on Wikipedia:
Why is MRI used?
MRI is an important tool both for research and clinical purposes. Even though most people don’t like being put in an MRI scanner, you might feel more appreciation when realizing what the alternatives to MRI would have to be. Without MRI, we couldn’t get clear pictures of what’s going on in your head! The alternative would be to actually open you up and have a look inside. CT scans can take images of the body, but they are not nearly as clear and detailed as MRI images are, and MRI scans can be performed over and over again without exposing your body to radiation (as opposed to x-rays and CT scans).
How does it work?
I’ve listened to hours of lecture regarding this question. I’m a nerd though, so I really enjoyed it! I’ll try to simplify things though, I promise.
By looking at the name, (Magnetic Resonance Imaging), we can infer quite a few things. Magnetic infers just what it sounds like – the machine uses magnets (BIG ONES) to take the pretty pictures. Resonance refers to radio frequency pulses which are emitted as a part of the process (more on that in a minute). Imaging, of course, is the end result we want. But we need to get down to an atomic scale to understand how it works. I’ll explain in steps:
- The human body is primarily composed of hydrogen atoms; these are the atoms which are used in MRI to take images. Hydrogen atoms are positively charged. The name for the process of an atom circulating around its own magnetic field (and they all have their own magnetic fields) is called precession. Precession works via a magnetic charge; the term used for this magnetic charge is called magnetic moment. In everyday life, all the hydrogen atoms in a human body are doing their own thing, having unique magnetic moments, precessing at different rates, having a good old time!
- When a body is placed in an MRI machine, all of the atoms are affected by the magnetic fields created by the magnets in the machine. They all line up like little tin soldiers, aligning themselves to the magnetic field created by the magnets in the machine. They will point either “up” or “down”, north or south. They go from being random to being one or the other.
- The machine emits a radio frequency pulse using the magnets. This positively charges all of the atoms, sending them into a sort of energized, excited state. So exciting!! They flip to the opposite direction of where they were lined up a moment ago.
- As the protons relax from the radio frequency pulse, an image is created by monitoring the amount of time it takes for the protons to relax and move back to the state they were in during step 2, aligning with the original magnetic field. The amount of time it takes to return to that state depends on the tissue the hydrogen atoms are bound in. This is kind of easy to imagine; different tissues like grey matter, white matter, cerebrospinal fluid in the brain’s ventricles, create different types of tissue. Anyway, an image is composed based on this.
Edit: I originally wrote this post when I had a bit of trouble sleeping, and mixed up the terms protons for atoms themselves! Made the appropriate corrections. Oh, science, why must you be so complicated? Don’t write things at 2am, kids! :)
And that’s it! After the images are collected a little bit of preprocessing is done, just to clean things up a little bit for doctors or researchers to see things more clearly… but by that point, whether you’re a participant in a research study or a patient getting medical tests done, you’re already out of that giant machine and on your way! It’s a painless process, you’re given earplugs to drown out most of the noise, and there’s no radiation involved. I honestly fell asleep during my brain scan (oh, what I do for research..). Oh, and by the way, all those loud noises the MRI machine makes? As far as I understand, it’s actually the sound of the magnets combined reacting to the different radiofrequency pulses. Bang, bang, bang! Cool science is loud!
It really is a crazy piece of technology, isn’t it? Again, this is a pretty simple explanation, but I try to not let these posts drag on. Again, if you have questions, feel free to comment or contact me!