How dangerous are magnetic items near an MRI magnet?
Why Hacker News recommends it
Linked in threads on magnets and implants as a vivid demonstration of how violent MRI magnet forces are.
What it is
A three-minute demonstration with a decommissioned 4 tesla MRI magnet showing how magnetic objects are pulled in and oscillate along the bore. It illustrates the safety hazards of ferromagnetic items near MRI scanners.
Recommended by 1 HN commenters across 1 different months, 2011 to 2023.
What Hacker News said
Recommends Shinkei · 2013-10 · on “Towards an inexpensive open-source desktop CT scanner”
A topic I can speak intelligently about! (I am a Radiologist.) This article is a great discussion of modern imaging technology and I 100% agree that MRI is incredible. But CT has become much more impressive than the single-slice scanners of yore. Watch this video of a modern scanner rotating at full speed: [LINK] Currently, the race to improvement is about speed and lower radiation dose. The newest scanners can take hundreds of 2D slices in a single rotation of less than a second and reconstruct the image with a huge variety of algorithms accounting for body part, patient size, etc. that all allow for lower dose and noise resulting in better diagnostic quality. MRI is truly the cutting edge
Cites po · 2011-12 · on “Dropping a Magnet Through a Copper Pipe”
They are superconducting magnets kept that way through cryogenic helium. They can lose their magnetism through a process called quenching. If you search on youtube for "MRI quench" there are several videos of people messing around with MRI's before they get decommissioned. Not exactly safe. [LINK] [this video] There is a lot of helium in there and it can explode: [LINK]
Cites phren0logy · 2012-03 · on “Body Hacking: Thoughts Regarding My Magnet Implant”
Obviously I have no first-hand experience with implanted magnets, but MRI magnets are generally getting stronger. What is safe for a 1.5 tesla MRI may not hold for a 3-4 tesla MRI. The rapid magnetic oscillation has been known to heat up wires and cause burns. There's some people horsing around with 4T MRI that might give you pause. [this video]
Cites ben_w · 2023-05 · on “DARPA’s silent MHD magnetic drives for replacing naval propellers”
"Trans-cranial magnetic stimulation" — it has both been called "the god helmet" and has been used in that way. IIRC it's a pulsed field to induce electric fields in your brain, and also has an extremely short range. Somewhat more significant to human health is that magnetic material can be rapidly drawn towards the magnets: [this video] At very high field strengths, you also need to account for "your blood is electrically conductive, and electrical conductors resist motion when in a magnetic field due to induced electrical currents". According to test subjects, this "tingles". At the most extreme fields strengths we can currently make, you also have to account for the water in your body being dia