From: NFetter <NFetter@aol.com>
Date: Wed, 7 Jan 1998 22:27:46 EST
To: pinhole@exploratorium.edu
Subject: Re: some bio-med questions, kinda
Hi Ellen,
Nuclear Magnetic Resonance is a phenomenon that results from passing a radio
frequency signal to the electrons in atoms. The simplest NMR involves hydrogen
atoms, which have only one electron. A radio signal of about 60 mHz inverts
the spin state of the hydrogen electron and when it returns to ground state
another radio signal is emitted that can be detected by an ordinary radio
receiver. When many electrons emit this signal, it is easy to detect. In the
old days (1960's) the sample to be examined had to be spun at high speed to
get a sharp signal. In the mid 1970's, Fourier transform NMR was invented,
which meant that the radio signal could be obtained rapidly without the need
for spinning. The NMR scanners for humans appeared in the 1980's using the
Fourier transform method. The hazard to humans is essentially zero unless you
are afraid of confined spaces. We are surrounded by radio signals all the
time. I forgot to mention that the environment of each hydrogen atom is
different, so the signal emitted has a slightly different frequency, hence the
NMR image you see in the scan.
Neil Fetter