Re: DeGaussing an MRI suite

["Brian Rees Lab" <brees@lanl.gov>]

Jim,

I occupied an office that had previously housed a powerfull magnet.  The
metal studs contained enough residual magnetism to affect a serious effect
on my computer monitor.  I never did get the fields measured though.  Moving
the monitor around caused effects that would have been pretty fun in the
days prior to urinalysis!


Brian Rees
brees@lanl.gov


-----Original Message-----
From: Jim Dunlap <jim.dunlap@guardian.brooks.af.mil>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Date: Wednesday, January 27, 1999 1:28 PM
Subject: Re: DeGaussing an MRI suite


>     Are you pledging a fraternity?  Periodically, a bunch of guys from one
>     of the ivy league schools send a letter to Ann Landers describing some
>     far-out, fabricated situation for her to reply to.  She's pretty good,
>     most of the time, about figuring out it was a joke.  Your question
>     reminded me of one I occasionally would get when teaching the
>     'uninitiated' lay person; viz., "What happens to the residual medical
>     x-rays that aren't absorbed."  My initial response was, "They bounce
>     off of the patient, settle to the floor of the diagnostic radiology
>     suite following patient exposure, and eventually are either swept up
>     by the janitor or evaporate, but if you need to enter the room it's
>     O.K.. because they'll just bounce off of you."  Then I would tell them
>     the truth.  With regard to your question, I really don't have an
>     answer, except to say I've never heard of residual "static magnetic".
>     (Thats kind of catchy.  Sort of like the internal dosimetry tables
>     that Ken Skrable developed which have been referred to as the "Scrable
>     Tables").  As an aside, but just a peculiar a phenomenon:  I was once
>     involved in a case with a hot cell where high-dose gamma sources were
>     handled remotely, in which the thick glass window, after MANY years of
>     exposure, 'shattered', due to being 'supersaturated' with electrons,
>     but remained in the solid physical form.  This apparently was because
>     the glass was acting as a capacitor, and finally became
>     'supersaturated', and "exploded", similar to what happens when
>     'radiation trees' are produced when a piece of plastic is exposed to a
>     very narrow beam of high energy electrons.  So, maybe your question is
>     valid.  I too would be interested in an accurate discussion of this.
>     Thanks.
>
>     jim.dunlap@guardian.brooks.af.mil
>
>
>______________________________ Reply Separator
_________________________________
>Subject: DeGaussing an MRI suite
>Author:  radsafe@romulus.ehs.uiuc.edu at guardian
>Date:    1/26/99 5:09 PM
>
>
>Has anyone has any experience in dealing with the residual static magnetic
>fields that remain in an MRI suite after a unit is removed?
>
>The residual fields can reach 2 mT.  This is too low to be a real health
>concern, but it's enough to cause problems for electronics and its enough
to
>upset people.
>
>Degaussing is theoretically possible, but I can't find anyone who has
actually
>done it.
>
>
>John Moulder (jmoulder@its.mcw.edu)
>
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