What's the difference between MRI and fMRI?

08 January 2012

Question

What's the difference between MRI and fMRI?

Answer

Chris - Well they both use the same principle - magnetic resonance imaging. Dave - Magnetic Resonance Imaging actually should be called nuclear magnetic resonance imaging but they took off the nuclear because it scared people even though it's not at all dangerous in any way, shape or form. What it's doing is looking at the nucleus of atoms. In fact, in MRI, it's looking at the nucleus, nuclei of hydrogen atoms. If you put them in a very strong magnetic field, it affects the way they interact with radio waves and then by an incredibly complicated bit of maths and some big computers, you can basically have different bits of your body in different strengths of magnetic fields which means that they interact with different radio waves and by keeping changes in the magnetic fields in lots of different directions and doing lots of hard maths, you can build up a picture of where all the hydrogen atoms are in your body and also, something about how they are chemically inside the molecules which they're sitting in. Chris - Yeah, that's basically what they're doing and if you want to do functional magnetic resonance imaging, what they are doing is looking at the level of oxygen which is in the blood and so, you infer how active, say you're looking at the brain and you want to know, is this bit of brain active when I do a certain job, you look at how oxygenated the blood is that's going through that area because an area of the brain which is more active uses more energy and it gets more energy by burning more glucose with more oxygen. Therefore, it augments its blood supply and you can use that as a measure. Dave - And I think there's a second thing which they can do which is, they can actually look at the flow of blood because they can kind of magnetise your whole body very quickly with radio waves and then they can look at how the magnetisation moves in your body and they can look at where that's moved and anywhere it's moved, there's probably will be blood flowing and so they can work out blood flow just by what's moved inside the body.

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