More about magnetism and MRI's
It came up here wrt my planned MRI that there seemed to be things not
made out of iron that were subject to magnets. By coincidence I came
From Wikip ... http://en.wikipedia.org/wiki/Ferrite_core
Ferrites are ceramic compounds of the transition metals with oxygen,
which are ferromagnetic but nonconductive. Ferrites that are used in
transformer or electromagnetic cores contain nickel, zinc, and/or
So I guess all these compounds and maybe more (that aren't used
commericialy or not in transformers) would be magnetic like iron, but
not containing iron, and to top it off, nonconductive.
What a complicated world we live in, where there are general rules and
exceptions to the rules.
Nowadays, people are most likely to see ferrite cores as the small
cylinders near the end of electric wires, such as USB cables, power
supply adapter cables, etc.
"hey have a low coercivity and are called "soft ferrites" to
distinguish them from "hard ferrites", which have a high coercivity
and are used to make ferrite magnets. The low coercivity means the
material's magnetization can easily reverse direction without
dissipating much energy (hysteresis losses), while the material's high
resistivity prevents eddy currents in the core, another source of
energy loss. The most common soft ferrites are:
Manganese-zinc ferrite (MnZn, with the formula MnaZn(1-a)Fe2O4).
MnZn have higher permeability and saturation levels than NiZn.
Nickel-zinc ferrite (NiZn, with the formula NiaZn(1-a)Fe2O4). NiZn
ferrites exhibit higher resistivity than MnZn, and are therefore more
suitable for frequencies above 1 MHz.
Just for the record, I was told the MRI machines were magnetic even
when they are off.. That's why I think they won't let me in the room
just to look at a machine with no one in it, until I've undressed.
They let me look at it through a window.
Yep. That is because it is never off, it is just in standby. From my MRI
safety lectures in the past, IIRC, to turn it all the way off there is
an emergency "quenching" that stops the superconducting magnets from
conducting but it take a while, and a whole bunch of money, to bring it
America is at that awkward stage. It's too late
to work within the system, but too early to shoot
Why don't you just tell the people at the hospital where you're going to
have your MRI done about your concerns. They may be able to give you
some idea of how to test to see if the MRI's magnetic field will affect
you BEFORE they sit you onto the table and slide you into the machine.
I did. Although it was an "Imaging Clinic", not a hospital. The
front desk at the orthopedist had detailed flyers for each of two
chains of such clinics here. .
You don't have to raise the subject. They do. There's a
questionnaire about whether you've ever worked with metal, and around
30 questions about what metal things you have in your body. There are
loads of things that surgeons lieave in people's bodies, on purpose.
Pins in their bones, staples, stents, blood vessel clips, even things
in people's heads. I'd heard of many of them, but not all.
But I don't have any of that, and the only question was, metal filings
in my eye. Both places asked the same question, and they were both
vague, imo. When I said I was just a hobbyist, maybe 3 hours of
grinding total in the last 30 years, the first place said, Don't
worry. It's for people who work with a grinder or sheers or a saw for
a living, 40 hours a week.
Couldn't take it at the first place because of claustrophobia. The
second place had a machine with a larger bore (but still closed.
Doctor insisted on closed, not open, because the image is much better)
And the moment I started to ask the same question to the woman on the
phone at the second place, she interrupted and said, You need an
orbital X-ray. The x-ray machine didn't move, so I don't know what
orbit they're talking about, but I think it's my eyeballs themselves
Yes, that's it. http://en.wikipedia.org/wiki/Orbital_x-rayhttp://en.wikipedia.org/wiki/Orbit_%28anatomy%29 The orbits are the
cavities in the skull where the eyes are found, and maybe they are
also the eyes. .
My eyes don't have any metal in them, andt it was worth one x-ray to
find out. And I'll pay closer attention from now on so I won't need
The second clinic depended on earplugs, which the tech said did a
better job of keeping the noise I heard down, and yet I could still
har him. Not good enough, and I frieaked out in about 5 minutes. I
thought all these places had headphones with music and even maybe
radio stations. I should have asked about that.
OK, I'll admit I'm having trouble with those formulae you posted.
I understand the character "a" to be a variable, but the formula doesn't
If you presume "a" is any number above one, the term (1-a) becomes a
negative number, suggesting you have fewer than zero zinc atoms in the
If you presume "a" is one, the term (1-a) becomes zero, and you have no
zinc atoms in the ferrite at all. It therefore consists entirely of
manganese and rust OR nickel and rust.
And, if "a" is any number less than one, you have zero, or fewer than
zero manganese or nickel atoms in your ferrite.
I'm certainly not a chemist, but that "a" character needs some
I just copied and pasted. I wanted to get MnZn and NiZn, and didn't
want to ship the rest of each sentnece. I don't know what a is, but
I have a feelling that the a in Mna in the first line should not even
After all, there is no a in the other one, NiZn. .....no, wait, there
is in the secone one after the word forumula. Okay, now I have less
than no idea what a means.
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