Hello to everyone.
I cannot thank all of you enough for all of the great information! I must
say that I have learned more in the last few days than I thought possible.
I have included a summary of the responses I received. I have also included
a couple of web sites for those of you who would like to read up on the
condition that is spawning this surgery and exactly what this surgery
involves - I found it to be rather interesting myself. As for those
concerned that my helper would be scared away, nope. She said that she has
been part of some rough fills, it will take more than this to do it!
This is a pdf document: <http://meddev-corp.com/PATIENTBROCHURE.pdf>
http://meddev-corp.com/PATIENTBROCHURE.pdf
As a warning, this web site contains pictures of surgical procedures:
<
http://www.blepharoplasty-eyelid-surgery.com/facial_nerve_paralysis.htm>
http://www.blepharoplasty-eyelid-surgery.com/facial_nerve_paralysis.htm
Thank you again You all are such a wonderful resource of information!!!
Adrienne
Summary of Responses
_____
Gold is absolutely non-magnetic. Even the things that they cut cold with
(for lower carrot) is non-magnetic. I've checked dozens of yellow-gold,
white-gold, and other jewelry many times and I've never found a gold allow
that was even slightly ferromagnetic.
_____
I'm am nowhere close to an expert on these things, but since gold is a
conductor, an eddy current will develop in the bar whenever this user moves
through a magnetic field gradient (think of the force when removing a
probe). Depending on the size of the gold bar, it may be insignificant, but
I'm not sure how to calculate the magnitude of the effect.
_____
As far as I know, there is no problem with Ag near magnets. One easy test
is to get a bar and place is directly on the magnet in question.
_____
Sounds like a bizarre procedure. Gold is not magnetic but moving metal in a
magnetic field generates voltage so there may be some felt response there.
_____
What's the difference between gold in the teeth and gold in the eyelid? But
who knows what a moving conductor will do in a strong static magnetic field.
It might be enough to cause voltages high enough to cause twitching. It's
all speculation but there is a body of knowledge out there and I suggest you
consult and industrial hygienist expert in magnetic hazards.
I believe these questions should always be left up to the experts and leave
the informed decision to them and the person affected. All you can
definitively tell her are the values of the fields she will be exposed to.
_____
Even though the metal is not magnetic a paramagnetic field will be induced
by the conductive electrons lining up with the magnetic field. This is why
an aluminum probe will not fall out of a magnet and why it is not
recommended for people with metallic implants to be in a magnetic field.
I would not recommend that she utilize the instrument. I've heard stories
where people have moved stainless steel implants by moving fast through 10G
field and would expect an eye to do something similar.
_____
The only concern I might have is that even though gold does not have
magnetic properties, it still conducts electricity. Depending on how intense
the field is, there is Lenz's Law to consider, in that a current will be
induced in a moving conducting object in a magnetic field.
The direction of the current will be in such a way as to induce an opposing
force to the direction of movement. This is why gradients in an MRI magnet
are so noisy - they are physically trying to jump with each pulse.
I've seen this demo in a horizontal MRI magnet, and I have to get really
close to the bore of a vertical magnet, but if you take a quarter
(non-magnetic), put in on its edge and tip it over in a strong magnetic
field, it will slowly fall over. That is Lenz's Law.
The other way I've seen it is with a sheet of thin aluminum pressed up
against that bottle of a magnet - let it drop. For the first couple of
inches away from the bore it slowly falls, then when it gets far enough
away, it then falls at a normal rate. Make sure it is not a steel plate or
you will be in trouble. (Also be careful of non-US coins - I am not sure,
but I think some of them might be magnetic).
I really don't know how close or at what field strength she might feel the
effects. Maybe an industrial hygiene officer or safety officer might be able
to shed some light on this.
_____
The problem would most likely not be the magnetic properties. Gold is not
magnetic at all. What could be an issue are eddy currents.
If the gold bar is large enough to weigh down the eye lid, it might exhibit
slight eddy currents. This is the effect you feel for example when removing
a probe from the magnet. The mass of metal and the speed of the object
affect the force exhibited on the object. Assuming that the bar is small and
your coworker will not move her head too quickly when in the strongest stray
field, there should not be a significant danger.
_____
Magnetic susceptibility for metallic gold is -28 x 10^-6. For comparison,
Al is +16.5, Cu is -5.5, Ag is -19.5, Pd is +567, and H2O is -13 (all x
10^-6). Gold plating is sometimes used on electronic contacts in probes,
and a susceptibility matched coil is plated with Pd, and these probes shim
well. I expect no measurable effect on a tiny gold bar in a fringe field,
but I'm not a real doctor. You might ask an MRIist.
_____
I expect you may hear from many married AMMRL members who will testify their
gold wedding bands have never given them a problem.
The problem this object could pose merely stems from its electrically
conductive properties. Wile not a problem in the NMR Facility, if she gets
an MRI, the gradients applied will induce electrical current in the bar,
causing it to heat. It's hard to say exactly how much its temperature will
rise, but I'd say it would be safest to avoid MRI's while the implant is in.
_____
Her physician should be able to better talk to her about this. MRI is now so
common that the medical community should have a lot of information about
biomaterials and their interaction with strong magnetic fields.
_____
Though Gold is non magnetic, it is highly conducting and depending upon the
strength of magnetic field, when the conducting bar moves in the magnetic
field, it may induce some current,may be very less, but it may irritate a
person. This is based on theory only. One has to see how tolerant the person
is to this current. If the bar is very short, most likely it would not have
any feeling of current flow in the eye lid.
_____
Even if the implant is 24 karat gold, the implant is metallic and, as such,
even if not ferromagnetic is subject to the potential for Lenz effect. For
such a small mass, the effect will undoubtedly be small, but in such a
sensitive area as the eye, I would be extremely cautious, even with the
greatest assurances from the physician.
It is very likely that this will be a complete non-issue. But provided the
physician provides an iron-clad assurance as to the non-ferromagnetic
properties of the implant, I would still be very careful. Depending upon the
shape of the implant, field strength, gradient and even orientation of the
implant relative to orientation of the magnet may impact the safety.
_____
You are right, pure gold is non-magnetic. Therefore, there is no danger that
the gold implant will be attracted to the magnet. However, you have to be
aware of another problem. I shall try to explain this as clearly as I can.
The problem has to do with eddy currents. Eddy currents are created in any
metal, when it moves in a magnetic field.
Conversely eddy currents are also created in a static metal object by a
moving magnetic field. In your case the former is the case.
In simple terms eddy currents are created in a moving metal surface because
by the motion, the metal is obstructing the lines of force.
This also means the eddy currents are orientation dependent. The effects of
eddy currents can be minimized by moving extremely slowly when she moves
near the magnetic field. As long as she doesn't climb onto the top of the
magnet and things like that she should be safe.
Again, since the size of the gold bar is small, the effect should be
minimal. Eddy currents are a surface phenomena. My guess is that the surface
area of the gold bar is very small, and therefore, the effect should be very
very small. I believe she won't notice the effect.
However, if she ever has to go for an MRI scan she should explain the
situation to her doctor; she may not be allowed to have an MRI scan because
of the expected effect of eddy currents form the rapidly switching
gradients.
I hope I haven't scared away your helper, but be careful; keep her as far
away from the magnets as possible, especially if you have any very high
filed non-shielded magnets. Even the shielded ones, once you get very close
to the magnet, have quite high fringe fields.
_____
It's not the same thing, but I've got lots of Hg/Ag filling and two gold
lined caps on my teeth without effect. The only person that I personally
knew who was effected by the magnet had a "stainless" steel plate in his
skull necessitated by a war wound. The only thing he noticed was some
resistance moving immediately next to the magnet.
Original e-mail:
_____
> From: Hoeglund, Adrienne
> Sent: Friday, July 01, 2005 7:54 AM
> To: AMMRL
> Subject: NMR and Gold Implants
Good morning to all.
I have a user that is going to have surgery on one of her eyes. She has
problems with one of her eyes not fully shutting. So, what the doctor is
going to do is implant a pure gold bar into her eyelid so that her eye will
fully shut. The bar is very, very small and is pure gold. I can not find
anywhere where it states that pure gold has any sort of magnetic properties
and shouldn't be near a magnet. Because I can't find anything, I thought I
would come to you all and verify that she shouldn't have any problems being
up next to the magnet. She helps me with fills so I need to be absolutely
certain she will be safe. Honestly, I don't believe there is a problem, I
just would like some input.
Thank you!!!
Adrienne
Adrienne B. Hoeglund
NMR Specialist
AOC, LLC.
950 Highway 57 East
Collierville, TN 38017
(901) 854-2800 ext. 532 - work
(901) 853-1582 - fax
www.aoc-resins.com
Received on Wed Jul 06 2005 - 12:37:58 MST