I don’t even know the right kind of flair for this question- tech? physics? biology?
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eta: thank you everyone! This is all very helpful. I was in the big MRI tube yesterday and had no idea how the technology actually worked. So cool!
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[MRI stands for](https://www.khanacademy.org/test-prep/mcat/physical-processes/proton-nuclear-magnetic-resonance/a/magnetic-resonance-imaging-mri) “magnetic resonance imaging”, and to understand why we use that tech for medicine, you have to understand a bit of physics.
Everything is a tiny bit magnetic. Iron is *especially* magnetic, but everything’s a little bit magnetic, so if you have a powerful enough magnet, it will “push” a little bit against everything, even the insides of your body. So an MRI machine starts by making an extremely strong **magnetic** field, and literally magnetizing your body. That’s the “magnetic” part.
The “push” of the magnetic field causes all the hydrogen atoms in your body to align in the same direction, like magnets lining up with one another (because that’s what they are, everything is a tiny bit magnetic).
And this is where the “**resonance**” part comes into play. The second step of an MRI machine is that it sends short pulses of a different electromagnetic field, pushing the hydrogen atoms into a slightly different direction. When that second pulse ends, the hydrogen atoms snap back into place, sending out a tiny electromagnetic pulse back of their own.
That feedback information, all the tiny electromagnetic pulses from all the hydrogen atoms snapping back into place… that’s what the machine uses to construct an **image** of the inside of your body.
The link above is to Khan Academy for a deeper overview if you want.
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