The excitation of atomic nuclei in MRI procedures is achieved by
matching the frequency of the incident electromagnetic radiation with
the corresponding "resonant" frequency of the target nuclei for the
chosen electromagnetic field strength.
The variation of resonant frequencies for varying field strengths is
different for the nuclei of different elements. In fact each element
(more accurately each isotope of each element) has its own
characteristic profile of "resonant" frequencies (called Larmor
frequencies after the British scientist Sir Joseph Larmor, 1857-1942).
A table of MRI (NMR) frequencies at different field strengths for
different elements can be found on the website of the Massachusetts
Institute of Technology at:
You can see that the field strengths for this table have actually been
chosen to match with convenient values of Larmor frequencies for
hydrogen - H(1).
So, for argument's sake, if an MRI scan was set up with a field
strength of 5.8717 Tesla and a frequency of incident radiation of 250
MHz, then you would expect the hydrogen nuclei in the region of the
body under examination to "resonate" accordingly.
However, you would not expect the nuclei of the mercury, silver or tin
atoms in your amalgam fillings to resonate significantly at all.
Many people mistakenly presume that the reason for this must be that
the field strength is not great enough.
But this is not the case.
The true explanation is that the combination of the frequency and the
field strength (both of which can be very precisely controlled) does
not correspond to the conditions required for producing resonance in
any of the atomic nuclei in the material which constitutes the
In our example (a field strength of 5.8717 Tesla), the Larmour
frequencies of Ag(107), Ag(109), Sn(115), Sn(117), Sn(119), Hg(119) and
Hg(201) are 10.116, 11.630, 81.749, 89.063, 93.181, 44.568, and 16.499
MHz respectively, and not 250MHz.
The Larmor frequencies for these nuclei will always be different from
that of hydrogen, whatever the strength of the field. And it is
therefore possible to ensure that only hydrogen nuclei are excited in
an MRI procedure simply by determining that the incident radiation
matches the Larmor frequency for H(1) at the chosen field strength.
However, I think that to suggest that this may be taken as a general
indication that electromagnetic energy is not capable of inducing
electrical currents in metal amalgam dental fillings would be silly.
Do you not agree?
Keith P Walsh
of course not. you have again grasped at straws and missed. the 250mhz
will induce currents in any conductor within range. and since fillings are
conductors they will have currents induced in them and these will of course
produce potential differences.
Do you think that it should be possible to determine whether or not
the electrical potentials thus generated in amalgam fillings are able
to dissipate electrical energy through the nerves in people's heads?
Keith P Walsh
it should be possible to determine that. i have had tests that measure the
normal nerve pulses and stimulated signals when testing for carpal tunnel
syndrome. there is probably no reason the same type of test couldn't be
used to test for nerve impulses in the head... there would be two problems
though, getting access to the nerves with the probes, and preventing
interference from the electromagnetic field you are testing with. there
would be a big problem with the probes actually injecting signals from the
emf instead of measuring the effect on the nerves themselves, some tricky
shielding or processing to cancel out the rf effects on the probes would be
needed to see the actual nerve impulses.
As an aside, I have read about people receiving radio broadcasts within
the vicinity of high power AM transmitters. Supposedly the corrosion,
of whatever chemical means, had created rectifiers. The resultant DC and
I suppose a loose part of a filling resulted in audio being generated
and conducted via bone to the inner ear. I have not experienced this.
If this is true, might not people who have this defect in their fillings
also experience some kind of sound. Or is the noise of the damn machine
so loud and synchronized with the "tooth generated" audio that it is not
detected by the patient.
The only effect I remember from the procedure is that I saw pink clouds
floating in a light blue background when I closed my eyes.
I might add that they found nothing wrong. But my left ear still rings.
Would you presume that the medical profession has enough scientific
evidence to conclude that the ringing in your ear is not the result of
a neurological injury caused by the discharge of elecrical energy
through the nerves in your head resulting from the generation of
electrical potentials by the metal fillings in your teeth?
Keith P Walsh
PS, remember that it has been demonstrated experimentally that metal
amalgam dental fillings generate electrical potentials with magnitudes
of up to 350 millivolts. See:
And the resting potential of the human neurological synapse is only 70
Do you think it's possible to pose these questions to the experts at
your local college/university?
Do you think it's possible to specifically identify which nerves YOU are
As I've mentioned previously, I have done just that. You could do it or
you could arrange to pay me for my time and effort. The price keeps
Keith, aren't you saying that the MRI process itself cannot be
taken as a negative on other types of EM radiation? It seems Dave
has suddenly focused in on the EM radiaiton in an MRI which is
probably a very small amount of energy. The point is what
the Magnetic field does during an MRI, not the tiny dose of RF
radiation they give you. Let's also not forget that this (magnetic)
field probably isn't switching at a very high rate at all, even if it
is large, (because, remember a constantly CHANGING field is need to
Good grief... An MRI will suck up a floor buffer; forget about it
rattling your fillings. Patients are constantly exposed to huge amounts
of EMR during an MRI. -- See:
http://www.simplyphysics.com/flying_objects.html# for some piccies :^)
An MRI will generate 25,000 times the earth's magnetic field, and aside
for avoidable mishaps, patients always survive. The human body is VERY
Sigh...Bill your understanding of physics seems to be a little, well
off. A magnet will fly into a refrigerator, that doesn't mean that
the magnet is generating any substantial emf in the refrigerator or
itself. of course if you spun the magnet around real fast so it
generated a changing magnetic field...
Magnets create attraction with magnetic materials because the little
tiny weeny magnetic domains align to become one great big, huge
magnetic domain when exposed to a magnetc field, no changing flux
Patients are constantly exposed to huge amounts
That is apparently caused by the magnetic field, not electromagnetic
radiation. If so you cold point an attenna at a
nail and watch it fly across the room. Do you see cars lifting up into
the air when they drive by a radiostation anntena, or a microwave dish.
That's EMR! My understanding
is that MRI's do not use substantial electromagnetic radiation but
only a little in the RF range. If they do, a lot of people would
like to know because on of the big selling points of MRI's is
that they are safer than x-rays because of the small-low energy
It's the change in the flux that matters, not the total strength
of the field, for the purpose of induced voltage. You would think that
for a while, while it powers up some voltage would be generated, but I
don't even know how long it takes the machine to reach full strength. I
could sit in a magnetic field 1,000,000 times the earth strength and
still not generate a voltage in a wire
A magnetic field attracts objects because they have miniature currents
loops inside them, aligned with exposure to the magnetic field and
force equals B(H)x(current). this is not the same mechanism by which a
magneic field induces a voltage. A changing
magnetic field will induce an electric field in AIR, but it won't
exert a force on the air molecules, otherwise we would have tornado's
near power generators!
Okay, lets simplify a bit. TAke two magnets near each other
and hold them in place with say a wooden clamp. Now you would
agree that the voltage one induces in the other is zero?
In fact it's obvious that since everything is static no energy
is being put into the system so it would be hard to see how a
voltage could be induced, if say one of the magnets was connected
in a loop with a wire and was doing work!
Now imagine the clamps were suddenly removed from the magnets.
Note that no voltage is induced, the instantaneous velocity
is zero, no change in flux going through the magnet etc, yet
there WILL be a strong force on the magnet. The generation of
force on the magnet is not the same thing as the induction of
voltage and current. Thus the fact that an MRI can exert a large force
on an object does not imply that it induces a large voltage,
although, when the object moves and depending on changes in the
field strength some production of voltage is likely to occur.
(I have no idea how much becaue I don't know that field strengths
and changes of the magnetic field in an MRI)
This concludes kindergarten physics 101.
Do you think that it would be possible to engineer a constantly
changing electromagnetic field which induces an electrical potential
in a metal amalgam dental filling?
And, if so, how might you determine what the characteristics of the
field should be for producing, say, the maximum effect?
Keith P Walsh
PS, further enquiries regarding the electrical properties of dental
amalgams can be found at:
At one time I could hear the local AM Radio station via the fillings in
my teeth. I lived fairly close to the transmitter. Proof is in the
pudding; potentials can be produced. A fork in contact with them could
also produce a current, quite uncomfortable at times, depending upon
saliva ph. I doubt however that there were any dangers involved in
either r of these side effects.
BTW, the wife was skeptical, so I convinced her by having her turn on
the radio to the local station. When repeatedly the song playing was
perfectly in sync with my ongoing rendition of it, she was finally
If however, yours is an attempt to produce some sort of panic over
amalgams, then I suggest that you don't get any, and then stfu about
those that other people have, because it isn't hurting you, nor is it
hurting them. I'm speaking from experience. The effects can be
irritating at times, however.
You able to actually hear the station? I wonder how that worked,
maybe the nerves in the ears where stimulated at the right frequency.
How did you know there was a correlation between salvia ph and
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