[TenTec] Induction Field [WAS - PS grounding]

[Steve Baron - KB3MM]

Looks like I got two of these for some reason.

----- Original Message ----- 
From: "Bill Fuqua" <wlfuqu00 at uky.edu>
To: "Steve Baron - KB3MM" <SteveBaron at StarLinX.com>; <tentec at contesting.com>
Sent: Friday, December 12, 2003 19:59
Subject: Re: [TenTec] Induction Field [WAS - PS grounding]


> MRI works by having a magnetic field gradient across the body so that the
> the hydrogen atoms in different location have different resonant
> frequencies. Then by exciting those resonances using a pulsed RF source a
> receiver can detect all the signals and using a FFT determine the
> frequencies produced.  Each frequency is associated with a particular
> location. The magnets have a very strong homogenous field but there are
> gradient coils that allow them to change the field gradient direction for
a
> different view you may say.
>
> 73
> Bill wa4lav
> At 06:34 PM 12/12/2003 +0000, you wrote:
> >Well, remember that all protons are not identical and one must use the
> >'magic individual combination of RF freq and field strength' to get a
proton
> >to flip.
> >
> >That simply means oine could keep the field constant and vary the RF freq
or
> >keep the RF freq constant and vary the field.  Really doesn't matter to
the
> >protons but one way may be much, much simpler to implement than the
other.
> >
> >BTW the percent change in one or the other is small e.g. about 0.1 %
would
> >cover all protons.
> >
> >----- Original Message -----
> >From: "David McClafferty" <ve1adh at yahoo.ca>
> >To: <tentec at contesting.com>
> >Sent: Friday, December 12, 2003 15:22
> >Subject: Re: [TenTec] Induction Field [WAS - PS grounding]
> >
> >
> > > I thought it was just the RF field that was changing
> > > within a steady magnetic field. Did some more reading
> > > and found there is a smaller magnetic field that is
> > > pulsed.
> > > I was wondering what the RF frequency was. It doesn't
> > > seem to be mentioned in anything I have read.
> > >
> > > Dave
> > >
> > >  --- Ken Brown <ken.d.brown at verizon.net> wrote: >
> > > 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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