Why are MRI's So Loud?

[Broomstick]

@Blue_Blistering_Barnacle

Lots of good answers above, in addition to these.

There are three ways to deal with this, AFAIK.

1. Ear protection. Pretty standard. (I’ve heard of using noise-canceling headphones, but not seen them much in practice- I think they’d be quite effective, assuming you could get electronics to work properly in MR environment.)

Noise-canceling works best with regular repeating noises. With an MRI you have the advantage that the system would know when the noise is going to start and the nature of it, given how controlled it needs to be to get the job done. On the other hand, as you note, the highly magnetized environment presents challenges to making this work reliably.

You certainly can have noise piped in to the environment - the headphones I had offered several music channels to help distract the patient from the experience and/or boredom - the tricky bit would be the precise delivery of the noise cancellation.

There’s a lot to be said for just plain blocking the noise, which is pretty fail safe and can be done with non-ferromagnetic materials.

2. Mechanical mitigation. Mostly stuff like more sound-proofing between coils and patient.

Um… I’m not sure there is the room in which to do that. It’s a pretty damn small space your looking at. There are already problems with some obese patients simply not being able to fit into the allotted space. Sure, it’s a great notion, and down the line it might be possible, but it’s tight fit already.

Sometimes making the resin holding the coils together stronger. A scanner came out in which the gradient coils were encased in vacuum. This was apparently quite effective, but (probably) makes for a smaller bore, which seems to bother patients more than the noise.

Yeah. I think a smaller bore would bother me more than the current noise level, which was largely mitigated by the headphones.

3. Advanced pulse sequence design. The noise occurs mostly because the gradient fields are “slammed on and off”, basically square waves (as much as possible). Newer pulse sequence designs (probably way more computationally intense to process into images) permit quieter or even silent imaging. They basically soften the edge of the gradient pulses, rounding the shoulders of the square waves. There is a loss of signal-to-noise ratio (about 10%), which is a drawback, because SNR is what it’s all about in MRI.

I’m not sure the SNR trade-off here is worth it. The whole point of advanced medical imaging is getting a clear view of what’s going on inside the body with minimal invasiveness.

But hey, I’m all for people trying to make stuff better. Go, researchers, go!

[Leo_Bloom]

@Broomstick

OK, let me see if I can construct an analogy that makes sense.

Imagine you are holding an aluminum can. By exerting a force on it by closing your fist sightly you get a sound flexing the metal. When you release your grip the metal flexes again and you get another noise.

In an MRI, the magnetic field(s) are likewise exerting forces on coils, which flex, and like the aluminum can, make a noise when the flex. When the force stops the coils flex back, making another noise.

But in an MRI the forces and the coils are enormously larger, so the noise is likewise enormously louder. And the force/release cycle is fast, so you get […sadly, a snip here, because I figure a mod would snip it anyway and Im saving them time].

Bravo.

Really. I used to be a typesetter and I like the creativity.

[Colibri]

@Broomstick

But in an MRI the forces and the coils are enormously larger, so the noise is likewise enormously louder. And the force/release cycle is fast, so you get BANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzng

…for however long it takes to make the images.

Moderator Note

I edited the oversize font to normal size. Please don’t post annoying fonts in GQ just to make a point.

Colibri
General Questions Moderator

[Blue_Blistering_Barnacle]

@Broomstick

OK, let me see if I can construct an analogy that makes sense.

Imagine you are holding an aluminum can. By exerting a force on it by closing your fist sightly you get a sound flexing the metal. When you release your grip the metal flexes again and you get another noise.

In an MRI, the magnetic field(s) are likewise exerting forces on coils, which flex, and like the aluminum can, make a noise when the flex. When the force stops the coils flex back, making another noise.

But in an MRI the forces and the coils are enormously larger, so the noise is likewise enormously louder. And the force/release cycle is fast, so you get **BANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzng
**
*WHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbingWHAMbing
*
BANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzngBANGzng

…for however long it takes to make the images.

Since Colibri took the effort to edit this post, I’ll add this:

I just have to point out that, at least for simpler types of scans, there are people who can hear all the whams and bangs and state what part of the pulse sequence is what.

Experienced MRI techs can pretty much tell what is being run by how it sounds.

[mixdenny]

@BrotherCadfael

I originally read this as “Why are MRAs so loud?”, which works, too.

I thought it was MREs. What in the heck are you doing to your “Beans, with tomato sauce and frankfurters”?

Dennis

[susan]

Huh. I’ve had several MRIs, and nobody played music OR offered me earplugs. I didn’t find it problematically loud, though.