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Why are MRI machines so noisy, and what stops us making them quieter?
Guy Inchbald
Upton on Severn, Worcestershire, UK
MRI stands for magnetic resonance imaging. The technique relies on the rapid switching of powerful electromagnets to scan your body. One set of coils creates a powerful, static magnetic field. A second set varies its strength rapidly up and down like a switch to superimpose variations on the main field, and in this way it controls the focus of the scan. These coils aren’t as powerful, but the variations are sufficient to generate strong mechanical forces on them. They are firmly fixed to the structure of the scanner, so they repeatedly push against it, making it vibrate.
The structure, in turn, pushes repeatedly on the air, which we hear as the buzzing sound. Anything that would quieten the buzz would either affect the magnetic field or block the hole we fit in, or both. Developers actually rewrote the scanning software to make the MRI machines sound less horrible.
When I was scanned once, the staff offered me headphones and piped-in music, but I refused because I wanted to hear what the programmers had achieved. I quite liked it, in a modernist, atonal kind of way – it was certainly preferable to a bit of Arnold Schoenberg.
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Anything that would quieten the buzz of an MRI machine would affect the magnetic field or block the hole we fit in, or both
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Jackie Jones
Brighton, UK
I don’t think MRI scanners are designed to be loud. It must be a by-product of their workings and therefore may be impossible to silence. But, having had lots of MRI scans, it just takes getting used to the noise. Even after removing my hearing aids and wearing earplugs and headphones, it is still loud. I now think of it as being in a modern music concert, as it is interesting how the frequency and volume of the noise changes, so I just lie there and enjoy it.
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