Been doing a little research, more to do, since posing MRI question. Seems
there is a high background field which is
held constant, for proton alignment. Then there is a time
varying field, much smaller, which modifies the overall field, allowing changes
in the precession which radiate RF.
I'm sure the details will prove even more interesting :-)
73,
-bob
>
> From: Ken Brown <ken.d.brown@verizon.net>
> Date: 2003/12/11 Thu PM 11:13:40 EST
> To: ve1adh@accesswave.ca, tentec@contesting.com
> Subject: Re: [TenTec] Induction Field [WAS - PS grounding]
>
> David McClafferty wrote:
>
> >To induce a current into a conductor the magnetic
> >field must be varying or the conductor or field must
> >be moving. The magnetism in an MRI machine is steady,
> >so unless they wheeled you in there quite fast, you
> >wouldn't get much current induced into your body.
> >
> >
> Excuse me, but if there is no change in the field, it will not make
> anything resonate. I'll look at the url you included later and see what
> they say. If they say that it is a constant, non varying magnetic field,
> then I say they are wrong. I took my VX-5 handheld radio and listened
> outside the lab while my wife was in the MRI machine. And I heard lots
> of varying pulse rates and bandwidth signals around the 60 MHz area.
> What I heard defininately came from the MRI machine, and it is not
> surprising that water molecules have a resonance around 60 MHz, human
> bodys being mostly water. Also the spare 3CX800A7s that I have for my
> Titan 425 are pulls from a MRI machine. If it was a constant magnetic
> field and not a varying one (at RF frequencies where ther are resonances
> with things in the body) they could just use a switch of some sort and
> not need a power amplifier tube>
>
>
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