How do MRI-compatible headphones work without metal?

[noahsdev]

So I had to have an MRI today and when your in the machine you wear these headphones so that they can talk to you and stuff, but how could they work with no metal? I realize that there are non-metal conductors but I thought that they had to be doped with metals (to make them semiconductors) so that they conduct well. I would keep voicing my ideas (I had a lot of time to think haha) but I really don't know what I'm talking about.
Does anyone know how they are made, or how they think they are made?
Just curious to know.

 

[Drakkith]

I thought it was only ferromagnetic metals that weren't allowed.
Now you have me curious.

 

[Baluncore]

I have seen a long plastic tube used for that application.

 

[Dale]

Baluncore is correct. Most MR headphones use a pneumatic tube for the sound. The speakers are actually located relatively far away, outside of the bore, and the sound is just passively piped into the headphones.

Drakkith is correct that only ferromagnetic materials have large forces on them, so you can have electronic devices inside the bore. For example, the coils that receive the signals are full of copper and semi conductors. However, that type of approach is rarely used for headphones.