Magnetic Effects

Douglas Rand drand at sgi.com
Sat Mar 1 10:41:48 EST 1997


Adam Reed wrote:
>...
> with the magnetic field of the MRI.  When the magnetic field is turned off,
> the water molecules will return to the relaxed state, resulting in the
> production of gamma radiation.  The body is the source of the gamma
> radiation.

Please read up on this before you scare someone.  The atoms don't reach
an excited state and as far as I know there isn't a sufficient energy
level in an electron's orbital state to cause a gamma ray (or even a
soft X-ray) to be emitted.

What *is* emitted by the aligned electrons (I believe it's just the
hydrogen atoms,  but my chem. courses are about 20 years ago) are radio
frequency radiation.  That's picked up by very sensitive detectors and
turned back into a 3d map.  There's no ionizing radiation involved at
all.

For the curious: As I remember this,  gamma radiation is defined as
radiation from nuclear events and things like particle destruction. 
X-rays are normally generated by momentum changes in electrons (usually
braking radiation as the electrons interact inelastically with an
atom).  The electrons involved in X-rays have been accelerated into a
target of a dense material,  titanium used to be the material of
choice.  I don't know about modern X-ray tubes.  In any case Nuclear
Magnetic Resonance (the real name for MRI,  but unused since "Nuclear"
scares everyone) doesn't involve accelerated electrons,  nuclear decay
or matter-antimatter anihilation,  so you're safe.

Doug
-- 
Doug Rand				drand at sgi.com
Silicon Graphics/Silicon Desktop	http://reality.sgi.com/drand
Disclaimer: These are my views,  SGI's views are in 3D



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