Subject: MRI technical question (Cook).
Date: Wed, 18 Oct 2000 140612 -0500
From: Roy Beavers
To: guru
--------------------------------------------------
..........From EMF-L........
I am not aware that we have any MRI expertise on this list to answer
this question...... I would like to know if it gets answered, because
we do often get questions about the risks of MRI......guru......
-------- Original Message --------
Subject: Re: ..childhood leukemia studies (Bowman)....
Date: Wed, 18 Oct 2000 11:18:47 +0100
From: Andrew Cook
Organization: Hummingbird-One
To: roy@emfguru.com
References: <39EB8224.CF068B9F@emfguru.com>
Dear Roy
A technical note (or more properly, a question, because I'm not a
physicist :
>From MRI theory, magnetism affects the precessed spin frequency of ions
with odd numbers of protons - in the case of the human body, this means
Hydrogen (dominant by a factor of about 1000 over the other isotopes
usually present). With a Gyromagnetic Ratio of 42.58MHz/Tesla, spin
precession frequencies will vary substantially according to the STRENGTH
of the
applied magnetic field. This MAY explain why (e.g.) Aluminium workers
have a relatively high (but NOT massively high) increased cancer rate -
IF it is the induced frequency which is pathological, rather than
the magnetism itself. The "safe" standard being set at
present for maximim EM exposure is of the order of 0.4mGauss, giving a
spin frequency of the order of 200Hz or less. I would suspect that
maximum pathological damage would be caused by a magnetic field strength
which produced a spin frequency which coincides with another dominant
external EM field - e.g. Mains (50 or 60Hz), or which takes the brain
out of Alpha state (i.e. creates a driving frequency which encourages
neural activity to remain in the relatively stressed Beta state at times
when it would otherwise not be). I also suspect that there are specific
frequencies which are vital to the rest of the body via the Autonomic
Nervous System. My maths and
physics is not up to the task of calculating this for alternating
magnetic fields, but I also could see that certain EM frequencies would
have a field strength band which would resonate with their signal -
causing maximum EM effect on anything containing Hydrogen ions. I
repeat that this is not necessarily a high strength field - in fact,
higher strength fields may be locally safer than intermediate strength
fields - but will always produce critical intermediate strength fields
at some distance from their source. I'm not sure what effect this
phenomenon would have at higher frequencies (e.g. Microwave) - is there
someone out there who can do the calculations?
The Geomagnetic field is approximately 60 microTesla (0.6 Gauss), giving
a
spin frequency of about 2555Hz. The present-day geomagnetic field
intensity is approximately 1% of its geological maximum. In order to
magnetically induce precessed spins of 15Hz or greater (i.e. Brainwave
frequencies in the Beta range), EMF's of between 0.35 and (say) 2.0
microTesla are required. It is interesting that most studies so far (?)
show that damage tends to occur more for exposures in excess of 0.3
microTesla.
regards
Andrew Cook
Archive provided courtesy of WaveGuide, http://www.wave-guide.org
Reprinted with permission of Roy Beavers, http://www.emfguru.com