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Comment by jonnathanson | Hacker News Reader

It's a cool idea, but let's not give short shrift to the MRI downside. MRIs are a big deal in today's medical world. Not being able to get one, depending on circumstances, can present anything from a mild inconvenience to a significant challenge. Especially if it's because of some piece of metal you elected to have implanted.

I type these words with a (non-elective) series of metal prostheses implanted in my hand and wrist. Luckily, I don't set off metal detectors unless they're turned to extremely high sensitivities. But MRIs are out. I don't want to get into TMI detail, but let's just say that I have an ongoing medical condition that makes the inability to get MRIs a big setback.

Tread carefully with this stuff. Look before you leap.

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There's a reason I have a Rod of Asclepius and "DO NOT MRI" tattooed on my wrist. Apparently it's quite possible to go through an MRI with implant intact, so long as the techs know about it. The inventor of these implants' advice about MRIs can be found here: http://www.stevehaworth.com/wordpress/index.php/welcome-from...

That is good to know. Thank you for the clarification. I'm glad the inventor took this into consideration.

> There's a reason I have a Rod of Asclepius and "DO NOT MRI" tattooed on my wrist.

You realize there are other large magnets in the world besides those for MRIs?

Yes, but how many large magnetic fields does one gets stuck into while unconscious that _aren't_ MRIs?

Besides, I've been exposed to serious magnets; the inverse cube law is my friend. Plus, even when I did come close to a strong magnet, all that happened was my implant flipped ends. In my finger, yes, but it wasn't painful (my implant is a cylinder, about as tall as it is wide; a disc magnet would have been much worse).

> Yes, but how many large magnetic fields does one gets stuck into while unconscious that _aren't_ MRIs?

If by "unconscious" you mean asleep, not many.

If by "unconscious" you mean unaware, plenty. Try walking past these in a lab:

http://www.youtube.com/watch?v=J2PDAnKEu9M

FYI: Neodymium magnet strength is of order 1T, same as MRI.

See where I mentioned the implant "rolling over"? That was caused by someone waving a stack of over 20 of these type of neodyms (http://www.magnets2buy.com/acatalog/neodymium-discs.html) within an inch of my finger. Those are so powerful that splitting a stack of 8 and letting them re-attract rejoins the stack with such force it smashes the magnets that make contact. So while I'm sure coming close to one of those would _hurt_, I don't think I'd either end up stuck to the magnet or having the implant dragged out of me.

The implant is powerful for its size, but its size is _tiny_ (half a grain of rice is a good comparison). It's not going to be as strongly attracted as that.

What do you have in mind? I can only come up with particle accelerators, nuclear fusion reactors and special cranes on junkyards..

High voltage transformers, demagnetizers (used in workshops all over the place), and large electric motors all come to mind.

They're rarely as strong as MRI magnets. My sister, who works as MRI technician, have seen MRI pulling with a blazing speed whole wheelchairs or heavy steel oxygen canisters from many meters away.

You can feel transformers from a (comparatively) massive distance away: I can feel a 230-to-12V transformer from 5 to 10cm, which is generally bigger than the transformer is. So you'd know to steer clear. I mean, IAmDann said here, http://www.reddit.com/r/IAmA/comments/g7lom/iama_24_year_old... that he can feel subway power transformers while walking down the street.

Demagnetizers... isn't the whole point to enclose the field? I'd also expect a warning sign or two, or for you to pay attention and know it's there. This is one of those "make your decision, and then live with it" things, and part of "living with it" is being aware of these things (and that acquaintances with more humour than sense might try to hand you magnets you can lift tables with).

Large electric motors... Dunno, have no experience of them yet.

I once broke my finger handling magnets from a really old hard drive. I don't want to think about what would have happened if I had magnets implanted in my fingers.

Do you get a sensation from switching power supplies vs transformers? Or is the frequency in a switching power supply too high to sense? (I've been studying power supplies a lot lately, so I'm curious.)

Tangentially on the topic of MRI safety, there's a fascinating story of a police officer who got too close to an MRI. The magnet yanked the gun out of his hand and the gun went off despite the thumb safety being engaged. (Nobody was hurt and the MRI received only superficial damage.) Apparently the strong magnetic field pulled the firing pin block out of the way, allowing the gun to go off. Details: http://www.ajronline.org/content/178/5/1092.full

Thinkpad switch-mode power supplies give almost no sensation, but I have gotten a distinct (and pretty distinctive) "buzz" from a Dell power supply. I'll point out others seem to be much more sensitive than I, as well (see jaa's comment, below; he can feel power cables. I can't). So the answer is... it depends? ",)

I'd like to contact you regarding how you went about getting your implant. My email is in my profile.

I'm sure it is, but apparently I can't see it, through either incompetence or measly karma. The short-form of my implant tale is here: http://discuss.biohack.me/discussion/comment/862#Comment_862

The emails in profiles are not visible to other users. This is a UI issue here that's bitten everyone.

Well now, isn't that something I should have checked. Capitalist.Carter@gmail.com

I have a magnet implant and looked into this. I found a study about MRIs and cochlear implants and not once did the study mention any dangers. Instead their concerns were based on demagnetizing the implant, and they found that the risk of demagnetization could be mitigated by aligning the patient in a certain way.

I know that cochlear implants are very different from finger magnets (cochlear implants are attached to bone) but it does challenge some of my basic assumptions.

It should also be noted that it would take less than five minutes to remove the implant with a scalpel.

A bit OT, but does it depend on the metal used? My wife's wrist was reconstructed using a set of metal plates after it was shattered a few years ago. However, she's had at least three MRIs (for an unrelated problem) since then. The plates may be titanium and not surgical steel, so perhaps that's the difference?

That's correct. Titanium is widely used for implants and is non-ferromagnetic so you can safely be MRI'ed with a titanium implant.

Isn't there inductive heating? It's conductive.

Yes, non ferromagnetic materials are still subject to some inductive heating due to eddy currents* but I have no feeling for how much.

*I've had the pleasure of being MRI'd a few times in a 4 Tesla research MRI (normal MRI's operate around 1.5T) and occasionally I would get nerve stimulation due to eddy currents set up in tissue. An interesting feeling!

Could be. I'm in a similar situation as your wife -- wrist and partial hand reconstruction -- but I'm under strict guidance to avoid MRIs, and have to report as such at hospitals and doctors' offices. I've also got a metal fixture in one of my toes on my left foot -- but, for whatever reason, that one's never caused an issue. Pretty sure the toe plate is titanium, and the assorted hardware in my wrist and hand are not.

Though it would seem that removing the magnet wouldn't be too much of a problem. I mean, it should show up under flouroscopy, and failing that, I guess you could mark the spot with tattoos with when get them implanted.

Would still be a headache though.

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