Magnetic force drops off with the 4th power of distance. What is a slight wobble is centimeters away from being a bullet. This is pretty easy to experiment with fridge magnets to build intuition. I would exercise caution if you have embedded magnets though.
"Don't take in ferromagnetic metals that would get pulled by a 3T magnet with 6 inches of separation" is a bit harder to grok for pretty much everyone.
What matters is the field gradient. The field inside the core of the MRI is pretty homogenous, so if the metal is in there when it's switching on/off then it's fine. They will put a precautionary shield over embedded shrapnel, but it's not a big deal- it'll just wiggle a bit, and can cause some image distortion. Heating would be caused by imaging gradients, which are very small precise fields layered over the main field. Imaging gradients can switch very rapidly, which is what could cause heating, but they're so weak (fridge magnet range) that it's a nonissue.
Likewise if you're more than about a meter away, the gradient has also dropped off and forces are much smaller.
Imagine a bubble around the entrance to the core: that's the danger spot where field gradients can be >3 T/m. Fun fact: take B^2/(2*u0) and you get units of Pascals. Magnetic pressure and fluid pressure can be thought about pretty similarly, except that free space is very impermeable and things like iron instead act like "holes" that can create strong flows between areas of different magnetic pressure. You can have a 3 T field separated from you by air, but if you stick a steel rod into it suddenly both ends of the rod will be at 3 T.
3 T works out to about 500 psi of magnetic pressure. If you have a small, 5 mm iron sphere in a 3 T/m gradient, the pressure difference across it is only ~2.5 psi. Size matters a LOT. 2.5 psi may be a slight tug; 50 psi may pull a wire straight through you. And 10 psi may be fine when it's embedded in you already, but given a distance to accelerate it can go pretty fast.
It can lift a paperclip, buckyballs stick to it, and moving the fingertip across devices - spinning HD's, laptops gives a sensation when the magnetic field changes. No real practical use but I knew that.
> The static magnetic field B_0 of an MRI machine attracts ferromagnetic objects and accelerates them toward the center of the bore of the MRI scanner. Ferromagnetic objects such as coins, hairpins, steel oxygen tanks or scissors can be accelerated or torqued by B_0 [4,10] and become dangerous projectiles [51]. The MRI safety program of the facility needs to warn about the misconception that larger objects will resist attraction to the field and need to emphasize the relationship between object size, material components, and projectile risk. Insufficient MRI safety training of ancillary medical personnel has led to fatal accidents when medical and other equipment was accelerated into the bore of the magnet [50,51].
X-rays would be no problem. Having something that is attracted by a magnet (such as another magnet) may cause an issue.
I don't have the biomagnet implants, I have the NExT RFID + NFC chip by DangerousThings in my right hand so its not as much of a concern.
Just go read straight from the source instead of linking research papers.
It has the warning of:
>MRI COMPATIBILITY WARNING The xG3 and all magnetic implant products should be removed before any MRI or magnetic imaging procedure. While our x-series transponders have tested as compatible with MRI machines up to 7T field strength, all magnetic products are incompatible with MRI machines and procedures.
> with people implanting rare earth magnets into the tips of their pinky fingers
And I was specifically referring to those rare earth magnets.
Your comment then:
> I have an implant and MRIs or Xrays cause zero issues.
You gave no indication about what type of implant you hand or its manufacturer, and replying to my comment I took it in context that it was a rare earth magnet.
Failing any information about the manufacturer, the information that I am able to provide to say "this can be dangerous" is research papers.
You have further clarified that you only have a RFID and NFC chip implanted and not any magnets ... and provided a link to another product (rare earth magnet implant) from the same manufacturer that indicates that it is indeed dangerous when near an MRI machine which agrees with the original comment.
MRIs don't accelerate objects instantaneously. If you look at the experimental setup, you'll see that they placed objects inside a pipe that allows them to accelerate with very low friction.
Implants inside the body cannot accelerate freely. They are held in place by the surrounding tissue. A force will act on them, and this force can cause complications, but implants will not suddenly turn into projectiles.
Not going to trust "newaccount74" with that info. It seems that the experts say that if the metal in the body is attached to bone (a screw or a plate), that is okay, but not if the metal is not permanently fastened to bone, so "surrounding tissue" is not going to stop the metal from causing problems.
>MRIs don't accelerate objects instantaneously.
See some of the videos below for evidence to the contrary. Large metal objects inside the room can definitely accelerate very rapidly and suddenly, and unexpectedly and has killed people.
Please re-read my comment carefully. I never claimed undergoing an MRI with metallic implants was safe, in fact I stated the opposite: "A force will act on them, and this force can cause complications"
The only thing I strongly disagree with is the urban myth that MRIs turn implants into projectiles. I don't think that can happen. None of the videos you linked show anything of the sort.
Yes, objects can be accelerated to dangerous velocities; but only if they can move freely (eg. oxygen bottles on a cart, wheelchairs, small objects placed on a smooth surface). Objects embedded in tissue can not move freely and won't start tearing holes in your body like reverse bullets.
It can of course still be dangerous. One lethal case documented in the literature involved a metallic clamp inside the patients head. The MRI seemed to have moved or dislodged it causing cranial haemorrhaging. It killed him, but it did not shoot out of his head like a bullet.
On the two occasions I failed to remove the large steel/titanium item in a piercing that set off the scatter machine so I was taken to a room and searched.
But the steel in my hands, the LED, chip and magnet in my left hand, the Vivokey and chip in my right hand - nothing. Even the handheld scanner doesn't pick them up.
One of the NFC chips was useful on my last trip to the US. I was constantly pulled over by the TSA and they might have wanted to inspect my laptop. So I made a backup, saved the minimum I needed, encrypted it on another device and uploaded to a domain. Clean installed the OS. The NFC chip carried a long string which to me gave the directory structure (very nested, no / in the string) and the encryption key. It wasn't needed, but it was amusing.
TSA scanners run around 30 GHz, which can only go ~1 mm into body tissue. It also isn't as high resolution as a camera, and objects a few mm wide won't get picked up well.
Imagine the joy of getting an MRI and forgetting about that bit of biohacking.