How do MRI Headphones work? (2022) | Hacker News Reader

How do MRI Headphones work? (2022)

tomlingham.com

212 pointskbf194 comments

>The only headphone tech that I was aware of or that I'd ever really considered

I guess I'm old now because this style of headphone was present on every model of passenger aircraft in the sky when I was a young adult.

When I was a kid, I once brought a stethoscope with me on the airplane so that I could watch the movie for free. (Or rather listen to it.) I pulled off the heart-listening cup part of the stethoscope and inserted beverage straws into the rubber tubing. Then I put one straw into each of the two little holes in the armrest.

It worked perfectly! Until a stewardess caught me and made me stop.

Thus sparking the engineer’s natural distrust of authority figures.

Sounds ingenious but I don’t quite follow the story. Why would a stewardess make you stop? Was there some system where you had to pay for headphones separately to hear a movie? I’m pretty sure all I remember are headrests having standard 1/8” audio jacks.

Yes, they would charge for headphones to watch the movie. The movie (there was only one, or maybe two on a long international flight) was played on CRT monitors mounted on the ceiling of each cabin section.

That was 20+ years ago, before flat panel screens in every headrest that could tune into one of a couple dozen looping channels, and long, long before you could watch anything at any time from a huge library.

You skipped too far into the future with the "huge library" bit. Fixed:

"long, long before you could watch [Season 2, Episodes 4 - 6 of Comedy Central Roast]."

Before that, they actually ran film projectors in some planes, using a variety of half-baked schemes.[0] Wild times!

[0]: https://en.wikipedia.org/wiki/In-flight_entertainment#Histor...

No, they had holes that sounds came out of and the headphones were just long tubes plugged into the hole to convey the sound to your ear. Like the article. They'd rent the headphones to you.

I used to just pull the armrest up next to my ear and listen directly out of the hole.

I would've moved you up to First Class for being so inventive.

I've never heard this before! When I started flying it was just the 2 mono jacks that you still see on planes that haven't been updated (always wondered why it wasn't just a stereo jack)

Pretty surprising to hear there's air/sound tubes rigged on to every seat on a plane.

Seems like the sound tubes ended in the 70's: https://apex.aero/articles/sound-tube-surprising-history-air...

> (always wondered why it wasn't just a stereo jack)

Either because they didn’t want you to take their headphones from the plane, or so they could charge for use because you couldn’t just plug in your Walkman headphones.

Or both.

I flew some overseas trips on Delta 767s in the late 1990s that still had the tube headphones. I was pretty intrigued by the concept, you could hold your hand up to the tube holes in the arm rest and hear the music echo off your hand.

Either on the headphones themselves or in the little overwrap bag there was a note to leave them on the aircraft when you deplane, because they (obviously) wouldn’t work elsewhere.

In my "maybe I'll need it some day" pile, I still have the two-mono-plugs to one stereo jack adapter I bought at Radio Shack so I could stick it to The Man. I think I only used it half a dozen times.

I bought a BLE wireless headset last year that came with one :-) No idea when I would ever need it!

> Seems like the sound tubes ended in the 70's

I was still encountering them in the early '90s, although by that time they had become uncommon.

I guess the article is written from the perspective of AVID: once electronic headphones became cheap enough, they didn't sell any more pneumatic systems for airlines - but the last planes equipped with pneumatic systems in the late 70s/early 80s still flew (unrefurbished) until the 90s.

> Seems like the sound tubes ended in the 70

I'm 40-ish, and I remember them as a child, so they were definitely still kicking around in the mid to late 80s, most likely on KLM and Pan Am, that were the airlines of my childhood.

They definitely were still a thing into the 90s

the inventing company is still around

https://avidproducts.com/2023/12/08/celebrating-70-years-of-...

apparently the speaker was in the armrest.

The only passenger aircraft I've ever encountered this on in 39 years of flying regularly were domestic US flights up until ~2000 or so. To the point where it's still a story I tell about the ridiculous levels of penny-pinching of US airlines (United wanted $5 to rent a plastic tube to let you listen to the inflight entertainment, with no way to plug in your own).

It was united that I most recently encountered this too. It was 2005ish and they flew a 747 with pull down theatre screens and pneumatic headphones on an australia-us flight.

Not sure if that was the backup plane or they were just desperately holding out to upgrade the fleet.

Having said that anyone that flew just over 30 years ago would have likely used pneumatic headphones and watched on a shared pulled down theatre screen. It was the norm not that long ago.

Shared screens was the norm in Europe too, but pneumatic headphones is something I've never seen on a European carrier at all - not at all ruling out some might use them, after all, there are many of them and I've by no means flown them all. I wonder, though if it's another case of tech that may have been skipped by airlines that e.g. didn't add inflight entertainment as early as others and so got to "skip ahead" a generation. Most of the European airlines I'd have flown with while younger would have predominantly flown short-haul flight where inflight entertainment might have not been a priority until fairly recently.

I haven't seen a inflight entertainment console in a few years of flying. There's a trend for some carriers in the US to remove them since most passengers would rather use their own tablet, phone, or laptop with much higher quality; and the carrier can sell them wifi.

https://www.forbes.com/sites/suzannerowankelleher/2019/10/13...

I've recently been on a plane which had some kind of small phone/tablet mount on the back of the headrests so that you could actually pull it down and put your phone/tablet on it to watch a movie. Great UX, because everybody is on their own devices all the time anyway.

I've also don't remember seeing them in Europe when flying as a child during the 1990s. Yes, there were shared CRTs every 10-15 rows or so, but the earphones were your run-of-the-mill electric earphones, usually with a two prong connector.

I have to add these were all international flights (this was mostly pre-Schengen, and in any case I don't believe I've taken a flight between Schengen Area countries until 2023), so I'm not sure if shorter distance flights would have been different. The mid-distance flights (> 2.5 hours) I've taken would generally have in-flight entertainment if it wasn't a budget option. Some of the cheaper flights had no screens (or maybe they had ones, but didn't want to pay for the movie) and still had earphones slots connect to a set of inflight radio stations (that were also available when there was a movie being played, as an alternative).

So yes, it was an arguably "superior" experience with selectable audio, volume buttons and rather crappy drivers directly inside the earphones.

I guess the airlines went with whatever was cheaper? For a while, pneumatic headphones (in a system with 100+ headphones) probably were cheaper overall than electronic ones, but with the constant decrease of electronics prices, by the 1990s they probably were only still there for legacy reasons...

Same experience here, never seen a "tube" type headphone on any European airline, but several carriers used weird headphone plugs so they could still sell you headphones.

I remember putting my ear up to the little holes and faintly hearing the audio even without anything plugged in.

Twelve channels of the weirdest and/or lamest music you'd ever heard in your life, all in a faint, tinny form that makes AM radio sound audiophile quality.

And, if you're lucky on a longer flight, the audio to a film selected to be inoffensive to everyone on the aircraft.

Sometimes in sync!

Yeah, on one armrest you had the sound-tube headphone "jack" and the other armrest had an ash tray. Wild times.

Does anyone know why old aeroplanes used the plastic tube style of headphones, instead of copper wired? From the blog post, it makes very good sense why the MRI headphones are necessary in that setting.

Edit:

From this URL: https://avidproducts.com/2023/12/08/celebrating-70-years-of-...

This type of headphones are called pneumatic headphones.

Spitballing:

Cost: one speaker and tubes was probably cheaper than 200.

Weight: old headphones were chunky, see above.

Comfort: not wearing giant chunky headphones you weren't accustomed to might have been preferable

Breakability: pneumatic headphones were harder to break, cheaper to replace

Stealability: passengers would have no reason to steal the headphones, and if they did it was cheap to replace.

All of these go away as proper headphones get increasingly small and cheap.

> Cost: one speaker and tubes was probably cheaper than 200.

I'm pretty sure there were 2 speakers in each arm rest. I think it's more about them being harder to break and cheaper to replace. When I flew on an airline that used them, they came clean in a sealed bag. They may have been brand new, or at least cleaned and sterilised. Electronic headphones are unlikely to be as cleanable.

Also possibly sanitation: You can probably throw the pneumatic tube headphones into boiling water without worrying about breaking any electronics.

I'm thinking I'm old too because I grew up with telephones that had crystal earphones connected with non-magnetic copper wire.

Yes— there was a time where the free headphones were this style and you could bring your own electrically conductive headphones (with the right adapter, since it had separate RTS jacks for left and right channels) to enjoy a slightly better and louder sound quality

This is certainly one of those things that has changed. I remember them too. A different era in flying.

I recall those being the standard for publci headphones everywhere, on planes, busses and hospitals

Hmm I can't recall my earliest flights (late 80s) but rapidly we had normal audio jacks

I was intrigued to see a lady at the crosswalk the other day wearing earbuds with thick tubing instead of wires. Googling it, I discovered they were "EMF free headphones". Apparently enough people think electromagnetic radiation in the ears is a problem that there are now dozens of these headphones on the market that put the driver half way along the cord, with tubes proceeding to the earpiece.

> Apparently enough people think electromagnetic radiation in the ears is a problem

Even Andrew Huberman, one of the most popular health science podcasters, has dabbled into anti-EMF quackery. On one podcast he claimed that his Bluetooth headphones produced notable "heat effects", implying that the electromagnetic energy was enough to produce palpable heat in his body.

It's obviously placebo effect to the extreme (physically impossible given the amount of RF energy) but nevertheless he made the claim. Millions of people listen to that podcast.

Of course, people are catching on that Andrew Huberman isn't really a good source of scientific information (nor really a good person, given recent revelations) but the damage is done.

If Bluetooth headphone batteries can produce significant heat for 8 hours we would have discovered a lot of free energy :-)

Ear warmers and headphones in one, that would be nice

Bluetooth ear warmers would be great if the Bluetooth bit could be made to work properly.

I've only watched a little bit of Huberman, but I can't take him seriously because:

a) he's obviously done a LOT of steroids or something, which aren't really great for you

b) At least half of what he says appears to be made up woo-woo nonsense

What are the recent revelations you’re referring to?

ny mag did a hit piece on him which seemed to be without much substance. First I've heard of him, no opinion at all about him.

I found it did have substance. The substance was that he is also a human being, and also flawed in his personal life.

That takes nothing away from his work in my point of view.

I don't understand why we hold impossible standards of perfection and sainthood to successful people.

Would you or I or anyone look less flawed if they went for us like that? Why believe ny mag? How would the author of that piece look under similar treatment? What consequences are there if the article is shown to be full of half truths and lies? By my reckoning, none. That makes it a hit piece.

He may be deeply flawed, he may not be at all. I have no opinion on it and lack the necessary information to form one, even if i wanted to.

NY mag’s reputation is the one damaged here in my eyes.

If you put yourself in the public eye I think you are inviting more scrutiny.

Is this the article everyone is referring to?

https://nymag.com/intelligencer/article/andrew-huberman-podc...

To me that is pretty much the definition of a hit piece.

Scanning through it, the allegations I spotted are:

* He is flaky and often doesn't keep appointments. * One guy says he invited him to go camping but didn't turn up * Apparently he may have slightly misled his ex about where he lived in private messages * His ex says that he has anger (purely verbal) issues * Some other people all say he has anger issues * Some incredibly spurious allegations that he had an affair

I probably missed some. But notably, almost nowhere is there any attempt to tell Huberman's side or have any empathy for him as a human being. Hence, it's a hit piece.

He tells stories about himself publicly and regularly. He has a forum to defend himself and gets value from what he does.

I see no indication that they approached him for comment, fitting your ‘hit piece’ comment, but does that matter? Is he off limits for some reason?

I would look much more flawed. I could not withstand the scrutiny of fame.

I do not see his reputation as damaged, I just acknowledge that he is not perfect, something I was sure about beforehand.

Can I know whether the information presented in the article is factual ? Of course not. Is it single sided or even intentionally harming ? Could definitely be.

> Even Andrew Huberman, one of the most popular health science podcasters, has dabbled into anti-EMF quackery. On one podcast he claimed that his Bluetooth headphones produced notable "heat effects", implying that the electromagnetic energy was enough to produce palpable heat in his body.

If this is true it take a lot away from his work in my point of view.

Well, non-ionizing radiation (NIR) cause cancer has being debated such as this [1]. It wouldn't surprise me that it will be a bit like the Roundup/Monsanto situation. I don't blame people wanting to use these kind of protection just in case.

And iPhone also had this in their Product Information Guide:

"When using iPhone near your body for voice calls or for wireless data transmission over a cellular network, keep iPhone at least 15 mm (5/8 inch) away from the body, and only use carrying cases , belt clips, or holders that do not have metal parts and that maintain at least 15 mm (5/8″) separation between iPhone and the body."

1. https://www.sciencedirect.com/science/article/abs/pii/S02697...

To be fair, EMF is 1/r^2 so the transducers (speakers) are indeed far from the ear. Not that they need to be, but...

It would be a real shame if EMF could propagate.

As long as it's slowly maybe you can catch it.

It it was at the speed of light we might have a problem.

Despite the questionable goals of the consumer, I have to credit hollow-tube technology as at least a reasonably non-fraudulent attempt to satisfy them.

In contrast, consider the glut of products involving magic nonsense about hematite beads or whatever.

They're also more durable; i.e. resistant to running over the tube portion with a chair.

They also use a similar mechanism for the "get me out of here ASAP" panic button [0] that staff place in your hand and tell you to squeeze if required, all it does is detect a change in air pressure on the other end of the tubing.

[0] https://www.mriequip.com/store/pc/MRI-Non-Magnetic-Magnalarm...

My house came with a button like that for the garbage disposal. Previous owner didn't like the idea of using an electrical switch with wet hands.

A button for garbage disposal before you have a chance to dry your hands? What does this button do, activate some pneumatic tube system so you don't have to carry trash to the bin?

They're talking about the "trash blender" that's common to be installed in American sinks

“Trash compactor”

It is an in-cabinet trash can with a mechanism to compress the trash when you push the button. I don’t know how common they really are. I’ve only know a few people with them. I could see where they might be more popular in apartments where you can’t easily take your trash to an outside trash can. They do require special, heavy-duty trash bags to handle the pressure.

What I'm talking about is an electric grinder that that sink drains into. Lots of people have them in the US.

I've always enjoyed the pun in the branding of "The InSinkErator."

Ah, we mostly call that a garbage disposal. They are very common.

Yes, the grandparent comment you're replying to also called them garbage disposal.

I sympathize with that, more than once I've eyed mine's regular-light-switch and thought: "Surely the remaining water on my hands has too much surface-tension to go through any of those tiny gaps in the plastic... Right?"

I believe this is required by code in some places, depending on the location of the switch. Mine is inset into the counter top, so plenty of opportunity for water to pool around it which I think would rule out an electrical switch.

Mine is also in the countertop, makes sense that code would require it in that case. Previous owner didn't like the idea of wet hands on a wall switch.

This guy also has a post about the hierarchy of socks and underwear which resonated with me.

https://tomlingham.com/articles/an-unfortunate-hierarchy-of-...

There's a sci-fi book I read a while back that had as a plot point an alien species that had algorithmically optimized its decision-making processes so much that it was no longer recognizably conscious. I think about that now and again when I get a little too invested in some system or practice.

Was it good? Do you have the title?

It was! The whole book plays a lot with various types of consciousness. Although that was a bit of a spoiler, so out of respect I'll give a somewhat obfuscated link and just say if you're reading something by Alastair Reynolds right now you should consider that before following the link:

https://openlibrary.org/books/OL26809698M

(Reynolds' got enough books in his bibliography I don't feel like I'm spoiling anything by mentioning his name - I suspect I could come up with any random plot point and he's probably written it in somewhere)

Ah, I thought this was going to be Karl Schrœder's Permanence, in which (unless I'm confusing it with a different book) a background point is that consciousness is only really useful in some niches, and most spacefaring species eventually lose it.

John Varley had a short story with that idea, too. A spacefaring race that is only conscious when needed. Good sarcastic lecture about how consciousness is overrated by those who have it.

Probably _Blindsight_ by Peter Watts

It was not, but that was also an absolutely fantastic book. I don't remember the sequel, Echopraxia, being as good, although there's a couple plot points from it that I do remember as weird ideas.

they may be referring to blindsight by peter watts

Interesting how different people's minds are.

I find the exact opposite problem, I go with old faithful over new.

It's for this reason that when I put my clothes away I simply take the stack of clothes in my dresser out, put all the fresh stuff on the bottom, then put the clothes that were in the drawer stuff on top.

I always grab the top sweater, t-shirt socks etc and I don't think about it at all.

FILO is not the standard method of maintaining one's stock of clothes? How else does a person mange wear leveling?

My process:

1. Buy ~15 copies of everything.

2. Not think about what to wear! Everything is roughly the same.

3. Throw out everything every ~3 years. A couple of months before that, start buying new models of clothes to find the best one.

4. Goto 1.

> A couple of months before that, start buying new models of clothes to find the best one.

This is so important. You'd think that manufacturers would just keep the same stuff for sale all the time for all time but it doesn't work that way. Lands End comes close for button shirts and wool trousers, but that formality level is wasteful for work from home.

Edit: At first the 15 copies seemed excessive since only 7 are needed for weekly laundry, but basically you can get 2x longevity out of the stock based on laundry wear.

Yeah, I'm absolutely pissed that New Balance had stopped making my favorite model of sneakers. I bought the last 5 pairs of them from a seller on eBay. Like, a model is great and it sells well, why would you stop making it?!?

> Edit: At first the 15 copies seemed excessive since only 7 are needed for weekly laundry, but basically you can get 2x longevity out of the stock based on laundry wear.

1 week of clothes does not provide enough safety buffer for forgetfulness and procrastination. Also, travelling.

Shoes and glasses frames are the worst for not being able to just buy the same thing for all time. Glasses have gotten better since I was a kid but shoes worse. I’ve given up on shoe aesthetics since Mizuno makes upgrades the same model with different colors. Looks like the current version of Wave Rider is 27.

Edit: Regarding total stock of clothes: this is a tricky balance between storage and wash cycle. Ideally I would do laundry nightly for day clothes and daily for pajamas so that no storage was necessary. With ~7 days storage already seems excessive since most days of the week there is more dirty than clean. It also only requires one load of laundry. With ~14 days that is twice the storage and while there are fewer batch operations there doesn’t seem to be a time savings since it would require two loads . . . Wait, do you scale in parallel by using a laundromat?

Lol, since we're going down this road... my clothing ends up getting stored more as a cache with an LRU policy. Every 6 months or so the items at the bottom of the drawer get assessed for eviction (donation). My favourite items are always on top, less used items are easy to find, and the unused items are easy to identify.

This is a much more efficient approach than Maria Kondo’s suggestion to hold each item up and determine its joy factor.

Do you not procure multiple copies of items that have a high value assessment?

I mean… I’ve got a bunch of fungible black t-shirts from Costco if that counts. They fit reasonably well.

There are a bunch of more expensive unique items too. I do actually find it a bit interesting to see which ones float to the top and which ones don’t.

Funny you mention Marie Kondo though. I do roll my clothes instead of folding them before putting them away into the cubes. I don’t entirely get it but it seems more space efficient that way.

Jeans get memoization! Wear them again before washing until something changes (e.g. spilled something on them) with an expiration time (e.g. 3 days or laundry day).

You shouldn't. If you successfully manage wear leveling all you've done is make sure you have to replace your whole stock at the same time, as well as depriving yourself of regular reminders of what new-ish clothes should look and feel like, leading you to keep wearing worn-out clothes.

> If you successfully manage wear leveling all you've done is make sure you have to replace your whole stock at the same time

I've been doing this for decades, but have never encountered this problem. I think because of a combination of the fact that I didn't buy my entire wardrobe all at once to begin with and that different clothes wear at different rates.

If your clothes are wearing at different rates then by definition you aren't wear-leveling.

I guess it depends on what you mean by wear-leveling. I interpreted it as wearing all of your clothes about equally as much.

With socks, wear levelling is actually really useful. I tend to buy a whole rotation of identical black socks, and then I don't need to pair them up individually. Also, buying 15 pairs of socks in one go isn't going to break the bank.

Wear leveling socks is a critical challenge for me. Unlike larger clothes, socks don’t stack easily, so defy conventional methods of stock rotation.

How do you approach this? Would it make sense to buy one of those shelf springs that grocery stores use to keep boxes towards the from of the shelf?

You need "Socks as a Service" (we could call it "SaaS") - every day someone drops off a new pair of socks and picks up your previous pair.

If you pay for a premium plan then no multi-tenanting and only you get to wear any particular pair of socks.

That sounds intriguing as I like not deciding. On the other hand, I'm sure SaaS has some premium over buying outright. Since I already have the capital outlay of a washer and drier and weekly time blocked for laundry of which socks is a very small percentage, I'm not certain if it would make sense.

On the other hand, if there is a "complete casual work from home uniform" service, that might be worth it as long as some VCs are subsidizing it like its 2019.

Heck, anything is worth it if VCs are subsidising it like it's 2019.

But what's the use in that "useful"? When I pick up a sock and it has holes, I throw it out. When the drawer gets empty enough it can fit another package, I buy one. What utility would come from worrying about when I used a particular sock?

It can be hard to find the same model sock when you need to restock. Wear leveling and replacing them all at once eliminates difficulty with matching. Also, if you don't wear level, you may have one new sock and one worn sock, and that can be weird.

Another benefit of FILO is to fulfill the social convention of wearing different colors. I purposefully acquire different colors of items in order to avoid drawing attention to my apparel. Fortunately my spouse tells me when clothes are worn-out so that isn't a concern.

Seems like people should diet and binge to purge clothing of the wrong size at various intervals.

Simply pop from the bottom of the dresser.

That method seems like it would have more cumulative effort than loading the cleaned clothes under the stack once a week. Additionally, I would probably rumple the stack pulling something out from underneath.

I use a queue of stacks for each regularly used item type. Laundry is enqueued on one end of the drawer and popped from the other, with stacks slid over as needed.

I wear whatever makes me feel good.

Haha, funny. It was just yesterday that I listened to a german kabarett recording which featured the fact that women are driving consumerism. And he used the exact same example: "When does he buy new clothes? When you tell him to! He would keep his current set for a lot longer." (translated from memory)

Your linked article confirms the semi-humorous statement just a day later.

Ha this is great! I completely relate.

There was a YouTuber (WhiteBoy7thSt if anyone is familiar) I watched over ten years ago now that came from very humble beginnings, and when he started to make real money, his first splurge (and one he stuck with) was new socks. When I say new socks, I mean new socks most days, maybe even a new pair for every day of the year. These were normal white socks, not any nice wool socks, so it was still fairly cheap, but when he grew up, they always had beaten, old socks.

This hits way too close to home. This was the thing I was going to do when I was rich, and now that I make enough money I barely even wear socks, lol.

God, this blog post is hysterical. It reads like a David Foster Wallace treatment! Next time he posts something good, please -- someone -- submit on HN!

It is wonderful and terrible to get clothing as gifts.

it seems 99% of gift clothing has some sort of special care requirements.

That’s why I always buy a “full” rotation. :)

Completely tangential story. A few months back I was getting an MRI. I stashed my belt, coins, keys, and phone. The machine started its clicking and thumping when I realized I had my wedding band on my ring finger. Immediately my mind raced to a video I once saw of an MRI machine propelling a fire extinguisher across the room. I braced for my finger to be torn off while I slowly took the wedding band off using only one hand. Luckily it stayed put through the whole scan and nothing happened.

If it was ferromagnetic you would likely feel it tugging as you got close to the magnet. Gold, silver, titanium are ok in MRI. However, next time, the second you realize you have metal on your person you should immediately inform the techs rather than try to just hold onto it! Aside from the risk of injury, it can be a real pain to get stuck items off the machine.

Taking off metal jewellery in the scanner is about the worst thing one can do - it’s then loose. It would be very unlikely to move from a clenched fist, even if ferromagnetic. However having it escape your hand isn’t that difficult.

I’ve seen most these things play out. And as you say, it’s exactly what the call bell is for.

I work on software for MRI machines, and one of the first things they do is high powered magnet safety training which is mandatory for everybody.

Even non-ferromagnetic materials react to the high field strength, and to show that, they let me hold a ring of aluminum just outside the bore. You can feel it "snap" to either parallel or perpendicular to the table when you try to turn it. It was a surreal experience.

I forgot to take my tungsten carbide wedding band off as well for an MRI, nor did the MRI techs say anything. It was in the middle of the MRI scan that I realized it was still on and then my fingers on the ring hand kind of started to feel fairly warm, but not certain it that was actually the ring picking up magnetic energy or if it was psychosomatic, but no harm became of it.

I looked it up afterwards and tungsten apparently as little to no magnetic effects, but depending on the amount of carbon used in it, it can.

Tungsten carbide jewelry is a mixture of tungsten carbide powder and a metal binder, typically cobalt or nickel. The metal binder is electrically conductive and thus susceptible to the induction heating you felt.

What you were experiencing was a) probably real and b) due to the conductive properties of the ring , not magnetic.

Oversimplification: Moving a conductor in a magnetic field or vice versa indices current in the conductor , resistance in the conductor results in heat.

The main field in an MRI is static but there are a lot of other fields moving around…

Similar happens on your body also (eddy currents) and deeper tissue gets energy which has to be controlled for - it can cause stimulation in peripheral nerves and heating .

> little to no magnetic effects

Whether or not it’s a conductor is probably more of a concern. The loop likely wouldn’t be large enough to cause any drama though.

Fun fact: metal being ripped away isn't the only negative effect possible, it can also heat up and burn you! (Why did I think this was fun again?)

https://www.sciencedirect.com/science/article/pii/S193004331...

https://www.washingtonpost.com/wellness/2023/07/26/mri-yoga-...

I got my third MRI after having a titanium plate put in my neck, and wow was I more nervous that time than the earlier two times. I made the tech let me test the panic button to prove it worked. Of course there was no problem with the MRI.

I asked about mine, and they said it was fine for the 1.5-tesla machine but they probably would have had me remove it for the 3-tesla one. I did feel it pulsing, but not noticebly warmer.

One of the things MRI do to create images is to pulse magnetic fields during imaging. These pulses are far weaker than the main field but will cause vibration of metals due to Lenz's and Faraday's laws. As the magnetic field changes it induces current in the ring, current in the ring interacts with the magnetic field to produce a (small) force on the ring. If you were getting a head/brain scan in a typical MRI your hand will lie near the locations within the scanner that see the largest swings in magnetic field. Beyond the vibration, rings are generally too small to be a heating issue even at 3T.

Best practice for at least a decade is to always remove all rings and all jewelry and failure to detect rings or other jewelry is generally seen to indicate a problem in screening. That is... if a radiologist sees evidence of a ring on the images there better be an explanation. The reality is that particularly older people have not removed their rings in decades and their joint disease may have expanded so much that it simply cannot be removed and the risk/benefit doesn't justify damaging the ring nor denying them the benefits of a scan. But if the patient can't take the ring off, the magnet wont either.

Just for reference, people get head scans with braces pretty regularly and it's not considered a safety issue. Braces and rings can affect image quality though so that's usually the concern. So if the ring is near the body part being imaged you'd probably be asked to remove it because they'll easily cause undesired issues (in, say, roughly a 3-6inch radius) that can result in images that radiologists deem unusable for making a diagnosis.

One of my favorite ISMRM posters that I saw in Toronto years ago was titled something like "a low-cost MRI-compatible communication system". It was really well written and you had to look at the photos to fully realize it was actually two Dixie cups connected by a string.

Man, you really nerd sniped me here. First: ISMRM means "International Society for Magnetic Resonance in Medicine" from here: https://www.ismrm.org/

I found a bunch of posters here, but I could not find the exact one that you mentioned:

https://www.ismrm.org/19/program_files/DP02.htm

Maybe lost now? Or a different page?

I'm pretty sure it was the 2008 ISMRM meeting (small chance it may have been 2003). I don't think it was actually submitted, because I couldn't find it in the proceedings even back then. I think whoever it was smuggled the poster into the hall and hung it among the others as a prank. I'm pretty sure the dead salmon fMRI poster was also there at the time but I can't remember if that was in the proceedings. The dead salmon fMRI did end up being published though and making quite a stir.

High-end headphone brand Audeze recently made an electrostatic headphone that works in MRI machines.[1] No air tubes needed and much better sound quality (and much more expensive).

[1]: https://www.audeze.com/blogs/audeze-journal/press-release-fo...

> [Audeze has since made an audiophile version, called the CRBN headphone, read that story here.]

Very vague explanation of how they work, and that link in the middle - I suspect that is the entire point of the press release.

Well it says the headphones are sold by the MRI company:

> The CRBN headphones are integrated into the Lumica AV system from SMRTImage that provides images and movies

Maybe you can get more info out of them: https://www.smrtimage.com/

I made the mistake of brining an episode of 99% Invisible to an MRI. The sound quality is so bad that you barely can't make out voices. It was excruciating to listen to something I could almost understand for that time.

I thought these were a nice idea when I had my MRI the other day, little did I know that I would barely be able to hear anything over the noise of the MRI machine. Ear plugs were better, kept out the noise of the MRI machine and let me drift into a trance.

I recently got an MRI and the technician asked me what I wanted to listen to on the headphones. I said "Something relaxing, do you have ambient music?". This turned out to be a terrible choice; the music was so quiet I could barely hear it. Earplugs would have been better. I had some in my pocket that I brought but it was too late.

So after the claustrophobic panic subsided and I realized I was left in there with nothing but the loud machine and my own thoughts, I decided to listen to the machine as if it were music.

I found it supremely hypnotic and trance-inducing, almost meditative. I'm a big fan of deep and hypnotic techno, so the rhythmic MRI sounds were right up my alley. I'd probably have enjoyed it more with earplugs though.

When I had an MRI a few years ago, my conclusion about the sound was "add a melody on top of that rhythm, and it would go over quite well in an underground industrial music club in an abandoned warehouse outside of Berlin."

I haven't looked to see if anyone has actually tried to make music with the sound or not.

When I had one it felt like I was listening to early to mid 2000s Autechre. In other words, almost interesting, almost enjoyable, just not quite there.

Answer seems to be, yes:

https://whyy.org/segments/the-mri-is-a-source-of-anxiety-and...

You can also make music with the scanner:

https://youtu.be/7MRm5mD2YxQ

> I said "Something relaxing, do you have ambient music?". This turned out to be a terrible choice; the music was so quiet I could barely hear it.

That was a golden opportunity to experience ambient music in the most historically authentic way possible!

Listen to Brian Eno's story of what inspired his 1978 album, "Ambient 1: Music for Airports":

https://www.synthtopia.com/content/2016/01/05/brian-eno-tell...

You're not alone. The "music" combined with the visual sensory deprevation can be a trip. Some machines are completely featureless on the inside and I've found it can feel like I'm floating in a bit open space, not crammed into a magnetic tube!

The strong field can induce vertigo as well, it's pretty weird. You don't even need to be in the scanner- the field itself causes it by mucking with your inner ear.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4362897

I get an MRI Brain every three months. I usually opt out of the piped music - mostly because it's either a bad choice by the radiology techs or tuned to a generically awful radio station - but the headphones lock into the head cradle so I use them with earplugs underneath. I close my eyes and tune out and try to not sleep (and twitch so they have to restart the capture).

Some of the pulse sequences are rhythmic and I find the entire thing somewhat meditative, but there are many other places I'd rather be.

This is exactly how I approached it the first time with just the ear plugs. I find those machine sounds can be quite soothing and hypnotic on their own. I’ll give the music a miss next time.

Earplugs and music is the discerning choice.

Most (all?) vendors suggest this - they get well over 100db and the vendor headphones are pretty crappy.

What was your experience with the MRI like? Specifically, did you "feel" it? I've had my knee scanned for ACL damage, and have spoken to a few other acquaintances that have had scans as well. We've all discussed having some sensation in the exact part of the body being scanned. We all just happened to similar sports based knee injuries. It was just the slightest of tingling, but noticeable. Definitely not painful or anything scary. Was it just psychosomatic? Very possibly, but it's interesting that we all experienced it.

The RF pulses and field gradients can directly stimulate the peripheral nerves. I have had involuntary muscle twitching triggered by many pulse sequences. It’s not unheard of. It made me more sympathetic for patients who have motion in images. It could be that the particular combination of pulse sequence and their nerves don’t jive and triggers movement.

Source: Radiologist (and personal experience in the bore)

If the patient isn’t twitching occasionally, the resolution is too low. We aim to be just below peripheral nerve stimulation threshold.

I’m sort of joking, but if you aren’t ever getting PNS, the machine is not being run very hard.

However the sensation you get in the region being scanned feels more like heating than PNS to me. You notice it more on high SAR sequences, suggesting that might be the cause. PNS just feels like twitching you can’t control, but ones milage may vary as this is anecdotal.

Source: MR radiographer.

I don’t think it’s heating. I think it’s PNS because my leg will periodically twitch which I can time with the pulse sequence.

I also have some small ACL reconstruction hardware in the knee which might interact and predispose that leg to moving…

I am well acquainted with high SAR abdominal scans in a 3T from my time doing scan certification in a petmr. Even though I “know” that tissue heating from high SAR is a thing, it always surprises me when my abdomen gets warm.

I used a high spec Siemens Avanto which a University owned. We used to get people complaining about PNS in the left hip and just above the bridge of the nose. It was a weird thing, and mainly happened on cardiac scans. Some found it too painful to continue with scanning.

I’ve had a little bit of PNS, but nothing that strong.

The SAR sensation of being heated from the inside is an unusual one, I’m not sure I’ve had anything else do that?

I had a head one done, it was very noisy, but the thing I found most uncomfortable, or rather, disconcerting, is when they injected the tracing fluid.

I thought they would do it all the way through, but then I suddenly heard the pump start halfway through the procedure and a slightly cooler fluid running up inside my arms.

I have had an abdomen MRI. I definitely felt sensations when the machine was doing particular sets of scans.

Also, I accidentally left my wedding ring on (I informed them, they were not interested in the slightest). My right felt hot during the scans. Not painful burning hot, but warmer than body temp for sure.

I guess forgetting your gold ring in an MRI lets you know it's not gold plating of a cheaper metal!

MRI can cause a tingling sensation. Apparently, it can be quite noticeable when you make a loop, e.g. with your arms. See peripheral nerve stimulation.

make a loop? wouldn't that require breaking the cardinal rule of not moving during the scan?

For my knee scans I could move into a position that was comfortable for me which actually I think was arms folded across my abdomen, but then you just do not move while the imaging is happening, which will have a distinct sound.

Ok, interesting, makes sense. Next, explain to me why the MRI machine does not... take itself apart? In an MRI machine without a cover you can see all kinds of micro and macro machinery, cables, fans, plating, sensors, magnetrons, pulse transformators, gun drivers... Pretty much each of those parts would be pulled through the room and get stuck to the MRI machine if brought in individually, or am I wrong?

https://www.google.com/search?q=mri+without+cover&tbm=isch

The engineers have accounted for this and appropriately fasten the individual components to the machine rather than bringing the parts in for assembling the machine while the high powered magnetic field is present.

I must be from a different era because a cup and string was well known as a kid as a way of transmitting sound. This is a very similar process.

Ahh, memories. Roughly 20 years ago, I took part in a research experiment which had as its aim to figure out which brain areas were involved when a blind person reads Braille. TL;DR: They had a hypothesis, which was mostly confirmed. It happens in the visual cortex. Anyways, back then, MRI was still newish tech. FMRI wasnt used much in typical medical settings, but for research. As part of the deal, the MRI technicians did share a lot of gossip and random knowledge during the rather long preparation times. Long story short, this is when I learnt about the tubed earphones. And all the other mechanisms which were constructed to transport the braille strip wthout operating a real motor inside the magnetic field... Was almost worth the 4 hours of having to absolutely lie still...

So how do the microphones that you use to talk to the tech in the MRI machine work?

> I'm not allowed to have any metals or magnetic materials on me.

Loose or easily dislodged materials. My belt buckle was ok to keep on. Had to empty my pockets, take off my ring, metal piercings are disallowed.

You don’t want gobs of belongings piling up on your magnet, and you don’t want something large enough to pin the human between it and the magnet. The first scenario is quite expensive to rectify. The second is quite expensive, quite painful, probably fatal, and certainly traumatic.

Also important: no fabrics with metal fibers.

https://www.ajnr.org/content/34/5/E47.full

Does this possibly depend on the field strength? I was asked to change into a hospital gown when I had an MRI a couple years ago.

This is standard practice at many places and should be standard everywhere.

The American College of Radiology say the below [1].

‘it is advisable to require that the patients or research subjects wear site-supplied MR Safe scrubs or gowns in place of their own clothing and undergarments in the region undergoing direct RF irradiation.’

Slightly odd - this appears to be about burns rather than projectile risk. Anecdotally, sites that don’t change patients have more accidents.

[1] https://www.acr.org/-/media/ACR/Files/Radiology-Safety/MR-Sa...

These are popular with two-way radios, where they're called acoustic tube earbuds.

I'd guess the tube is longer in an MRI, though.

TV presenters often use them; presumably the clear plastic tube are supposed to be harder to see.

Interesting, sound kind of like a stethoscope.

I bought a kind of unusual type of headphone from aliexpress a little while ago, that essentially consists of an induction loop you wear round your neck and tiny magnets you put in your ear, I'm somewhat scared to try them out as I don't especially want them to get stuck in my ear.

Tangential, I saw an episode of House where he put a patient with medical implants into an MRI and they ran it for a few seconds till the burning was too painful. Was this realistic?

It happens sometimes. I’ve been there for it with an infected filling (patient was unaware - they went to a dentist and reported back), with tattooed eyebrows and anyone with a cochlear implant tends to suffer (from the torque, not heating).

There is the odd burn - rare, and mostly preventable. Burns are the most common class or MRI injury.

I’m an MR tech.

I remember there was an episode where this happens with a prison tattoo-- some of them can contain heavy metals that react in an MRI.

I haven't flown for many years; but I think I remember airline headphones that were connected to the seat-handle with a hollow plastic tube.

They were awful.

This is exactly how headphones on passenger airlines worked several decades ago, until about 1990.

So they work like a stethoscope.

Would they sound better if they used a liquid instead of air for the conduction?

Probably not, recall how sounds sound underwater, they do not sound like they do above it.

Sound underwater loses energy in all directions whereas sound in a tube with water just propagates along the path.

What options exist for something superior? These headphones are awful

MEMS https://usound.com/usound-introduces-patient-safe-mems-louds...

Datasheet (PDF) https://usound.com/download/achelous-datasheet/?wpdmdl=746

Electrostatic headphones: https://www.audeze.com/blogs/audeze-journal/press-release-fo...

You can technically alter the sequence to make the scanner itself produce music. I don't know if anyone actually does this...

https://pubmed.ncbi.nlm.nih.gov/26178439/

Stimulating the audio processing part of your brain directly with the MRI machine.

Hire a non-metal band to play for you in the room.

tldr it's a pneumatic tube like a stethoscope. these used to be used within aircraft as well for inflight entertainment.

I used to love trying to surreptitiously unplug my traveling companions’ headphones so I could blow into the end of the tube. Never once pulled it off.

I've been on an airplane that used these! I think it even had a channel selector near the plug if I remember correctly (it's been a while).

I remember being able to select the pilot coms. I was nervous on my first flight as a kid, and it was very calming to hear the preflight checklist and ATC communication in the classic pilot cadence. This was pre 9-11.

I did wonder on my last flight if I could use SDR & android to listen in.

You can just use LiveATC on your phone these days, since many flights now have gate-to-gate Wi-Fi.

I think it's not allowed to actually operate a radio receiver on an airplane in the us: https://travel.stackexchange.com/questions/2322/can-i-listen...

Some airlines might still have the "listen to ATC" feature available, but in my experience, it's the pilots' decision whether that's available or not, and I've only ever been able to use it on a United flight once.

Sirius XM on JetBlue also has an "ATC channel", but I've only ever heard silence there, and I'm not sure if that's a similar thing (i.e. sourced locally), or just a random ATC feed from somewhere in the country relayed via satellite.

EDIT i'm wrong the speaker was inside the armrest.

I wouldn't be surprised if the channel selector wheel was a simple mechanical acoustic coupler rotating to connect or cap upstream source tubes. I remember it as well flying in the late 80s or early 90s.

> a simple mechanical acoustic coupler

I get what you're saying, and I think that's plausible. But as far as I'm concerned, an acoustic coupler is/was a type of modem, into which you plugged an ordinary telephone handset. You had to have a telephone that had hemispherical mike and earphone; it didn't work with e.g. a trimphone. Expected performance: 9,600 bits-per-second.

"coupling" then, whatevs.

lemme see if I can dig up a patent number for the channel switcher wheel and put this pondering to rest.

seems the inventing corporation is still around haha

https://avidproducts.com/2023/12/08/celebrating-70-years-of-...

Yep right next to the ashtray.

> The sound is transported along the tube via air — a very simple solution. Though this also explains why they sound absolutely terrible.

I see it is simple, but I wonder, would it be possible to use different sound medium ("conductor")? Some liquid, water perhaps? Would elasticity of the tube eat more signal than is lost in the air? Too heavy? Leaky? Questions…

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