On 19/04/2023 07:12, Roland Perry wrote:

Once upon a time I used to teach engineers how to repair mainframes.

And there were two things we stressed:

When working on stuff with powerful magnets in (such as are used for voice-coil positioners on hard disks) take off all rings and bracelets
etc, even if you don't think they are magnetic. Because they might be.

When working anywhere near to the TTL power supplies (5v, 200A) again
take off anything which might be conducting.

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger is
evidently fatter than it was - and it's definitely non-magnetic. I
checked. They also quizzed me about all sorts of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring to make
it into a magnet.

Andy

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 24/04/2023 21:54, Vir Campestris wrote:

On 19/04/2023 07:12, Roland Perry wrote:

Once upon a time I used to teach engineers how to repair mainframes.

And there were two things we stressed:

When working on stuff with powerful magnets in (such as are used for
voice-coil positioners on hard disks) take off all rings and bracelets
etc, even if you don't think they are magnetic. Because they might be.

When working anywhere near to the TTL power supplies (5v, 200A) again
take off anything which might be conducting.

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger is
evidently fatter than it was - and it's definitely non-magnetic. I
checked. They also quizzed me about all sorts of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring to make
it into a magnet.

I'm a bit surprised that they would let you in with any metal on.

A wedding ring can be rather dangerous in powerful RF fields. I think
the RF power used in MRI is low enough not to be a threat but the wild
changes in magnetic field might be. You can hear the thing creaking and groaning as the magnetic fields are ramped up and down violently.

Injuries in MRI scans due to having metallic bits in contact with skin
are more common than you might think. OTOH a wedding band is small
compared to the dangerous antenna length of ~10" or 5" where resonance
is possible and a serious threat (depending on the MRI used).

https://mri-q.com/rf-burns.html

--
Martin Brown

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 2023-04-25, Martin Brown <'''newspam'''@nonad.co.uk> wrote:

On 24/04/2023 21:54, Vir Campestris wrote:

On 19/04/2023 07:12, Roland Perry wrote:

Once upon a time I used to teach engineers how to repair mainframes.

And there were two things we stressed:

When working on stuff with powerful magnets in (such as are used for
voice-coil positioners on hard disks) take off all rings and bracelets
etc, even if you don't think they are magnetic. Because they might be.

When working anywhere near to the TTL power supplies (5v, 200A) again
take off anything which might be conducting.

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger is
evidently fatter than it was - and it's definitely non-magnetic. I
checked. They also quizzed me about all sorts of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring to make
it into a magnet.

I'm a bit surprised that they would let you in with any metal on.

Indeed. A friend of mine was refused an MRI yesterday when he turned up, because he didn't have documentary proof that a cataract operation he
had previously had didn't leave any metal in his eye, despite the fact
that as far as I'm aware cataract surgery does not involve leaving any
metal in the eye (and you'd be able to tell if it had, by looking).

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 25/04/2023 10:31, Martin Brown wrote:

On 24/04/2023 21:54, Vir Campestris wrote:

On 19/04/2023 07:12, Roland Perry wrote:

Once upon a time I used to teach engineers how to repair mainframes.

And there were two things we stressed:

When working on stuff with powerful magnets in (such as are used for
voice-coil positioners on hard disks) take off all rings and
bracelets etc, even if you don't think they are magnetic. Because
they might be.

When working anywhere near to the TTL power supplies (5v, 200A) again
take off anything which might be conducting.

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger is
evidently fatter than it was - and it's definitely non-magnetic. I
checked. They also quizzed me about all sorts of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring to make
it into a magnet.

I'm a bit surprised that they would let you in with any metal on.

Does that include amalgam fillings?

--
Max Demian

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 25/04/2023 13:57, Max Demian wrote:

On 25/04/2023 10:31, Martin Brown wrote:

On 24/04/2023 21:54, Vir Campestris wrote:

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger is
evidently fatter than it was - and it's definitely non-magnetic. I
checked. They also quizzed me about all sorts of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring to
make it into a magnet.

I'm a bit surprised that they would let you in with any metal on.

Does that include amalgam fillings?

There's more metal in my teeth than wrapped around my finger.

OTOH they were scanning my lower back, and I put my hands outside the
scanned area. I made damn sure that I wasn't wearing trousers with any
metal zip or button, and I left my jacket with my wife in the waiting
room. The woman who was next was in a hospital gown - I suspect an
underwired bra had to come off... I didn't look closely.

Andy

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 2023-04-25, Vir Campestris <vir.campestris@invalid.invalid> wrote:

On 25/04/2023 13:57, Max Demian wrote:

On 25/04/2023 10:31, Martin Brown wrote:

On 24/04/2023 21:54, Vir Campestris wrote:

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger is
evidently fatter than it was - and it's definitely non-magnetic. I
checked. They also quizzed me about all sorts of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring to
make it into a magnet.

I'm a bit surprised that they would let you in with any metal on.

Does that include amalgam fillings?

There's more metal in my teeth than wrapped around my finger.

OTOH they were scanning my lower back, and I put my hands outside the
scanned area. I made damn sure that I wasn't wearing trousers with any
metal zip or button, and I left my jacket with my wife in the waiting
room. The woman who was next was in a hospital gown - I suspect an
underwired bra had to come off... I didn't look closely.

I'm not sure you could keep your hands sufficiently far away from the
scanner, unless you are talking about prosthetic limbs that can be
completely removed.

In Brazil earlier this year, a lawyer (see! this is on topic!) was
killed when he took a loaded gun into the MRI room - and he wasn't
even the patient.

https://uk.news.yahoo.com/lawyer-died-concealed-gun-fired-111121257.html

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 25/04/2023 13:57, Max Demian wrote:

On 25/04/2023 10:31, Martin Brown wrote:

On 24/04/2023 21:54, Vir Campestris wrote:

On 19/04/2023 07:12, Roland Perry wrote:

Once upon a time I used to teach engineers how to repair mainframes.

And there were two things we stressed:

When working on stuff with powerful magnets in (such as are used for
voice-coil positioners on hard disks) take off all rings and
bracelets etc, even if you don't think they are magnetic. Because
they might be.

When working anywhere near to the TTL power supplies (5v, 200A)
again take off anything which might be conducting.

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger is
evidently fatter than it was - and it's definitely non-magnetic. I
checked. They also quizzed me about all sorts of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring to
make it into a magnet.

I'm a bit surprised that they would let you in with any metal on.

Does that include amalgam fillings?

They are small enough and not so very conductive so only mess up the
local field a bit but a loop of pure gold or silver is really very
conductive and capable of becoming red hot under the right (wrong)
excitation by either resonant RF or rapidly changing magnetic fields.
(or shorting out some beefy mainframe computer PSU or big battery)

--
Martin Brown

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Vir Campestris <vir.campestris@invalid.invalid> wrote:

Max Demian wrote:

Martin Brown wrote:

Vir Campestris wrote:

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger
is evidently fatter than it was - and it's definitely
non-magnetic. I checked. They also quizzed me about all sorts
of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring
to make it into a magnet.

I'm a bit surprised that they would let you in with any metal
on.

Does that include amalgam fillings?

There's more metal in my teeth than wrapped around my finger.

OTOH they were scanning my lower back, and I put my hands outside
the scanned area. I made damn sure that I wasn't wearing trousers
with any metal zip or button, and I left my jacket with my wife in
the waiting room. The woman who was next was in a hospital gown -
I suspect an underwired bra had to come off... I didn't look
closely.

I recently had an MRI of my brain (I guess to check to see if I had
any left). I have silver and gold in my mouth, and that didn't seem
to cause any problems.

--
Stu
http://DownToEarthLawyer.com


--
This email has been checked for viruses by AVG antivirus software.
www.avg.com

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 2023-04-25, Stuart O. Bronstein <spamtrap@lexregia.com> wrote:

Vir Campestris <vir.campestris@invalid.invalid> wrote:

Max Demian wrote:

Martin Brown wrote:

Vir Campestris wrote:

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger
is evidently fatter than it was - and it's definitely
non-magnetic. I checked. They also quizzed me about all sorts
of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring
to make it into a magnet.

I'm a bit surprised that they would let you in with any metal
on.

Does that include amalgam fillings?

There's more metal in my teeth than wrapped around my finger.

OTOH they were scanning my lower back, and I put my hands outside
the scanned area. I made damn sure that I wasn't wearing trousers
with any metal zip or button, and I left my jacket with my wife in
the waiting room. The woman who was next was in a hospital gown -
I suspect an underwired bra had to come off... I didn't look
closely.

I recently had an MRI of my brain (I guess to check to see if I had
any left). I have silver and gold in my mouth, and that didn't seem
to cause any problems.

It's only ferromagnetic metals that matter - but obviously hospitals
will very much want to err greatly on the side of caution.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 26/04/2023 00:09, Stuart O. Bronstein wrote:

Vir Campestris <vir.campestris@invalid.invalid> wrote:

Max Demian wrote:

Martin Brown wrote:

Vir Campestris wrote:

I've just had an MRI scan.

My wedding ring won't come off - the first joint of my finger
is evidently fatter than it was - and it's definitely
non-magnetic. I checked. They also quizzed me about all sorts
of possible implants.

I could feel the ring vibrate.

Presumably the fields were inducing enough current in the ring
to make it into a magnet.

I'm a bit surprised that they would let you in with any metal
on.

Does that include amalgam fillings?

There's more metal in my teeth than wrapped around my finger.

OTOH they were scanning my lower back, and I put my hands outside
the scanned area. I made damn sure that I wasn't wearing trousers
with any metal zip or button, and I left my jacket with my wife in
the waiting room. The woman who was next was in a hospital gown -
I suspect an underwired bra had to come off... I didn't look
closely.

I recently had an MRI of my brain (I guess to check to see if I had
any left). I have silver and gold in my mouth, and that didn't seem
to cause any problems.

It messes up uniformity of the magnetic field gradient in the vicinity
of the fillings but the effect scales as distance cubed so MRI can
tolerate it. Brain tissue is far enough away from teeth.

What you really don't want is a long thin piece of metal or a loop that
is resonant at one of the frequencies that they are using.

That's why I am surprised they let him bodyscan with a gold ring on.
(OTOH the ring it turns out was not in the scan region but outside)

Even so they don't like any unknown metal in the room with the big MRIs.
A big analytical chemistry MRI I know of has a serious dent in the outer
shell after snatching a scaffold pole that was passing by outside.
Nobody though to warn the scaffolders that there was such an enormously powerful magnet just inside the room and it was on the second floor.

Cockup on the risk assessment there but fortunately no-one was hurt.

This was back in the days when MRI magnets were not so well shielded and
there was a steel spanner chained to the wall by the door just out of
snatch range for demonstrating the magnetic field to visitors and VIPs.
It would appear to levitate if moved within snatch distance.

Every tool in the room had to be certified non-magnetic.

--
Martin Brown

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)