MRI scan

Things that work with electromagnetic fields…

I was therefore somewhat surprised when the paperwork for Anne’s first MRI said to bring some music as the machine is noisy. Of course, when you turn up there is zero provision for playing anything!

Things that work with electromagnetic fields, exposed to an electromagnetic field that’s akin to comparing a tangerine to a jumbo jet.

Then presumably the “things” they provided to go against/over the ears were driven through air pipes from an external source well-removed. The Radio 2 they were playing seemed very far-away!

Does not seem beyond the wit of man to devise something noise-cancelling.

Anyway, are piezo-transducers sensitive to magnetic fields?

Noise cancelling works by having a microphone located in the headphones (at least one per ear, possibly more) which records what is happening outside in order to create an opposite sound wave inside the headphones. The result, by the time it reaches your ear, is the two (external and internal) have largely been cancelled out. Microphones work magnetically.

As for piezo, no, they aren’t sensitive to magnetic fields. The long lengths of wire that might bring the audio to your ear would be subject to induction.

Likewise, if you managed to make a little piezo-ceramic microphone and a piezo speaker, then you would have to figure out how to make an amplifier work that isn’t affected by those magnetic fields.

It is perhaps worth stopping to think about why we have a machine that can pass radio waves through the body to create a complex three dimensional image…and yet the restful sounds in the headphones are quite literally pumped in by air. It isn’t that the headphones were an afterthought.

The Radio 2 they were playing seemed very far-away!

Possibly for the best considering the normal R2 content :)

Anyway, are piezo-transducers sensitive to magnetic fields?

How were you proposing to drive the transducers? Down a long wire?

Not that induced fields are a problem at all, much: the first MRI at our place (1980’s) was housed in an extension of the X-Ray dept. which unfortunately placed it about 30ft away from the Neuro-physiology EEG dept. and all the displays in their EEG kit shifted sideways on the screens.
They moved EEG…

Not that induced fields are a problem at all,

The one(s?) at the hospital in Rennes are housed together with the CT scanner(s?). Not sure how many of each there are. There’s also a Roboknife radiological surgery machine.
They’re all underground, in a separate building, a reaonable distance away from other parts of the hospital, with thick lead lined walls ¹, faraday cage built into the concrete ¹, and thick swing doors like something you’d expect to see at the entry to a nuclear bunker.

¹ As explained by one of the geekier doctors as she stopped to one-shot an espresso.

They’re all underground, in a separate building, a reaonable distance away from other parts of the hospital, with thick lead lined walls 1,

Lead and paper.