From Newsgroup: rec.crafts.metalworking

FYI.

Man wearing heavy metallic necklace dies after being sucked into MRI
machine, Madeline Halpert, BBC, 21 July 2025.

.<https://www.bbc.com/news/articles/cx2n39dvp0po>

Freak accident for sure, but MRI magnets are *exceedingly* strong, and
no they cannot be turned off.

Joe
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From Newsgroup: rec.crafts.metalworking

In <a9328ktck8aaea6p37a9lvvkmtb9gqb7st@4ax.com> Joe Gwinn <joegwinn@comcast.net> writes:

FYI.

Man wearing heavy metallic necklace dies after being sucked into MRI
machine, Madeline Halpert, BBC, 21 July 2025.

.<https://www.bbc.com/news/articles/cx2n39dvp0po>

Freak accident for sure, but MRI magnets are *exceedingly* strong, and
no they cannot be turned off.

Umm, yes, they can. An emergency shutdown is very expensive...
--
_____________________________________________________
Knowledge may be power, but communications is the key
dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]
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From Newsgroup: rec.crafts.metalworking

On 7/23/2025 9:30 AM, Joe Gwinn wrote:

FYI.

Man wearing heavy metallic necklace dies after being sucked into MRI
machine, Madeline Halpert, BBC, 21 July 2025.

.<https://www.bbc.com/news/articles/cx2n39dvp0po>

Freak accident for sure, but MRI magnets are *exceedingly* strong, and
no they cannot be turned off.

Joe

I saw that headline. Didn't read it.
--
Bob La Londe
CNC Molds N Stuff

--
This email has been checked for viruses by AVG antivirus software.
www.avg.com
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From Newsgroup: rec.crafts.metalworking

On Wed, 23 Jul 2025 22:48:47 -0000 (UTC), danny burstein
<dannyb@panix.com> wrote:

In <a9328ktck8aaea6p37a9lvvkmtb9gqb7st@4ax.com> Joe Gwinn <joegwinn@comcast.net> writes:

FYI.

Man wearing heavy metallic necklace dies after being sucked into MRI >>machine, Madeline Halpert, BBC, 21 July 2025.

.<https://www.bbc.com/news/articles/cx2n39dvp0po>

Freak accident for sure, but MRI magnets are *exceedingly* strong, and
no they cannot be turned off.

Umm, yes, they can. An emergency shutdown is very expensive...

How long does it take?

Joe
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From Newsgroup: rec.crafts.metalworking

On Wed, 23 Jul 2025 15:52:44 -0700, Bob La Londe <none@none.com99>
wrote:

On 7/23/2025 9:30 AM, Joe Gwinn wrote:

FYI.

Man wearing heavy metallic necklace dies after being sucked into MRI
machine, Madeline Halpert, BBC, 21 July 2025.

.<https://www.bbc.com/news/articles/cx2n39dvp0po>

Freak accident for sure, but MRI magnets are *exceedingly* strong, and
no they cannot be turned off.

Joe

I saw that headline. Didn't read it.

You should. It's short and free. And not so many folk realize that
those warnings are not just safety nuts nattering.

Joe
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From Newsgroup: rec.crafts.metalworking

"Joe Gwinn" wrote in message news:lps28k5hvrp6iegkb1slf45g4a7j7qifil@4ax.com...

On Wed, 23 Jul 2025 15:52:44 -0700, Bob La Londe <none@none.com99>
wrote:

I saw that headline. Didn't read it.

You should. It's short and free. And not so many folk realize that
those warnings are not just safety nuts nattering.

Joe
----------------------------------
I used that tech in an NMR machine while a chemist. The magnetic field was
of similar strength, 1.4 Teslas, and would bend the blade of a knife held
near it.

NMR is Nuclear Magnetic Resonance, a name that had to be changed for medical use to avoid frightening patients.

Someone else forgot to remove his wristwatch when changing samples and magnetized it. He took it to a jeweler to be demagnetized, which normally makes the watch vibrate a little at first. In this case it flew off the machine and landed on the floor, breaking its crystal.

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From Newsgroup: rec.crafts.metalworking

"Joe Gwinn" wrote in message news:lps28k5hvrp6iegkb1slf45g4a7j7qifil@4ax.com...

.. And not so many folk realize that
those warnings are not just safety nuts nattering.

Joe

------------------------
https://www.yalemedicine.org/news/mri-safety

In addition to the magnetic field that attracts iron, an MRI has a strong RF field that can heat a metal conductor even if it isn't magnetic. https://mriquestions.com/radiofrequency-waves.html
"The amplifiers used in modern MR systems typically produce peak power in
the range of 10-30 kW.."

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From Newsgroup: rec.crafts.metalworking

On 7/23/25 7:41 PM, Joe Gwinn wrote:

On Wed, 23 Jul 2025 22:48:47 -0000 (UTC), danny burstein
<dannyb@panix.com> wrote:

In <a9328ktck8aaea6p37a9lvvkmtb9gqb7st@4ax.com> Joe Gwinn <joegwinn@comcast.net> writes:

FYI.

Man wearing heavy metallic necklace dies after being sucked into MRI
machine, Madeline Halpert, BBC, 21 July 2025.

.<https://www.bbc.com/news/articles/cx2n39dvp0po>

Freak accident for sure, but MRI magnets are *exceedingly* strong, and
no they cannot be turned off.

Umm, yes, they can. An emergency shutdown is very expensive...

How long does it take?

Joe

I did an emergency discharge on a 3 tesla 6" room temperature bore
supercon once in grad school. There was a vacuum leak in the cryostat
and the boiloff rates had gotten high enough that it had to be shut down
and we didn't have a power supply to do it. We were trying to borrow a
supply from the system vendor but couldn't get one in time. Oxford had
an emergency procedure in the manual that used cross coupled stud diodes
rated for the main coil current (30 or 40 amps?) on a heat sink along
with a little dc supply and clip leads to energize all the shim and main
coil superconducting switches. Took us an hour to scrounge the parts
and a few minutes to get the charging wand inserted and connected. The
actual discharge took about 20 minutes for the field to be weak enough
that you couldn't feel it tug on a screwdriver held against the side of
the cryostat (not inside the bore). We let it go 2 or 3 hours just to
be safe, then burped a small hit of helium gas into the cryostat to
spoil the vacuum and boil off the rest of the LN2 and LHe. It was all
room temp a week or two later when we tore it down to replace the magnet.

That was back in the early 1980's. I've seen pics of MRI machines with
the diodes on a heat sink hung on the cryostat along with a discharge
cable for the charging wand that already had all the superconducting
switch leads tied together and a 5 volt power supply for the switch
heaters so it was all ready to go in case of an emergency. That plus
the normal charging wand and down it comes. An MRI magnet would have a
lot more stored energy than our little 3 T magnet so I'd guess at least
an hour or two to get the field down to where you could remove a large
iron object like a fire extinguisher (or a person with a large ferrous necklace :-)) and 24 hours to be sure it was completely discharged.
--
Regards,
Carl
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From Newsgroup: rec.crafts.metalworking

"Joe Gwinn" wrote in message news:0os28k59qdiq3bpm48osj752st7p2fd72q@4ax.com...

How long does it take?

-----------------------------------
The superconducting coil is a large inductor that stores up to a few kilowatt-hours of energy in its magnetic field, like a spinning flywheel. De-energizing an MRI magnet requires dissipating energy comparable to discharging a trolling motor battery or cooking a meal. Also inserting resistance into the coil creates an IR drop voltage the coil's insulation
must withstand.

The closest I've come was building a machine for GM that simulated releasing the energy in an alternator rotor's magnetic field if the battery cable disconnected. The model was a corroded connection and a bumpy road that
caused rapidly repeating load dumps.
https://en.wikipedia.org/wiki/Load_dump

As I watched my machine melted their surge protection after a few cycles. I think the result was the change to side terminals.

https://www.mgexp.com/forum/other-vehicles.69/gms-absurd-side-post-batteries.2305264/
"You know that the reason for the side post terminal was to prevent the corrosion which was a part of most top terminal installs after a few years. Side terminal batteries seldom have terminal corrosion issues in my experience."

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From Newsgroup: rec.crafts.metalworking

On 7/23/2025 6:14 PM, Jim Wilkins wrote:

"Joe Gwinn"-a wrote in message news:lps28k5hvrp6iegkb1slf45g4a7j7qifil@4ax.com...

..-a And not so many folk realize that
those warnings are not just safety nuts nattering.

Joe

------------------------
https://www.yalemedicine.org/news/mri-safety

In addition to the magnetic field that attracts iron, an MRI has a
strong RF field that can heat a metal conductor even if it isn't magnetic. https://mriquestions.com/radiofrequency-waves.html
"The amplifiers used in modern MR systems typically produce peak power
in the range of 10-30 kW.."

That second part is interesting. I have one titanium rod, four titanium
pins, maybe some brass fragments in my leg (mostly removed), and had a
couple pins in my two front teeth, but they may have been mostly removed
when I had porcelain crowns done.

I have been inside an MRI machine, but the order of things escapes me.
Time and temporal juxtaposition is a bit of a blur for some things in my
life.
--
Bob La Londe
CNC Molds N Stuff

--
This email has been checked for viruses by AVG antivirus software.
www.avg.com
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From Newsgroup: rec.crafts.metalworking

"Bob La Londe" wrote in message news:105tomg$p1i6$1@dont-email.me...

On 7/23/2025 6:14 PM, Jim Wilkins wrote:

https://www.yalemedicine.org/news/mri-safety

In addition to the magnetic field that attracts iron, an MRI has a strong
RF field that can heat a metal conductor even if it isn't magnetic. https://mriquestions.com/radiofrequency-waves.html
"The amplifiers used in modern MR systems typically produce peak power in the range of 10-30 kW.."

That second part is interesting. I have one titanium rod, four titanium
pins, maybe some brass fragments in my leg (mostly removed), and had a
couple pins in my two front teeth, but they may have been mostly removed
when I had porcelain crowns done.

I have been inside an MRI machine, but the order of things escapes me.
Time and temporal juxtaposition is a bit of a blur for some things in my
life.

Bob La Londe
--------------------------------

The MRI radio frequencies are between 50MHz and 300MHz. The shortest wavelength, at 300MHz, is 1 meter so your metal parts were likely too small
to be efficient dipole antennas.

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From Newsgroup: rec.crafts.metalworking

In <105s0c2$15m9u$1@dont-email.me> "Jim Wilkins" <muratlanne@gmail.com> writes:

[snip]

I used that tech in an NMR machine while a chemist. The magnetic field was >of similar strength, 1.4 Teslas, and would bend the blade of a knife held >near it.

NMR is Nuclear Magnetic Resonance, a name that had to be changed for medical >use to avoid frightening patients.

THANK YOU for using the proper name!
--
_____________________________________________________
Knowledge may be power, but communications is the key
dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]
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From Newsgroup: rec.crafts.metalworking

"danny burstein" wrote in message news:105ud2q$ihb$1@reader1.panix.com...

In <105s0c2$15m9u$1@dont-email.me> "Jim Wilkins" <muratlanne@gmail.com> writes:

[snip]

I used that tech in an NMR machine while a chemist. The magnetic field was
of similar strength, 1.4 Teslas, and would bend the blade of a knife held >near it.

NMR is Nuclear Magnetic Resonance, a name that had to be changed for
medical
use to avoid frightening patients.

THANK YOU for using the proper name!
-----------------------------------------

The choices were to change the scary word, or try to calm patients by explaining an interaction between Quantum Mechanics and electromagnetic
field theory, notice that I didn't try here. It's still NMR to chemists who understand how it works.

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