X-Message-Number: 3502
From: Brian Wowk <>
Date: Sun, 18 Dec 94 01:24:08 CST
Subject: SCI.CRYONICS Magnetite and Brain Mapping

        In response to Thomas Donaldson's recent speculations about
engineering bacteria to contain magnetite to enhance MRI visibility:
Such bacteria exist naturally.  There is a species of bacteria
found in some swamps (I can't remember the name) that contains 
enough magnetite to actually orient and change swimming direction
according to the Earth's magnetic field.  The magnetite particles
are prominently visible on electron micrographs of these bacteria.
        In fact recent research is revealing magnetite-based
navigation to be nearly ubiquitous in the animal kingdom.  For
some reason only primates seem to have lost this natural internal
compass.  No trace of magnetite has ever been found in human brains.  
Although I sometimes wonder whether the intense vertigo some people
(like me) experience in high magnetic fields could be caused
be a residual field orientation sense. 
        Getting back to MRI, magnetite-labelled antibodies are a
hot new research area in MRI contrast agents right now.  People
want to use these molecules as probes for (among other things)
determining the efficacy of gene therapy in treating conditions
like familial hypercholesterolemia.  
        Even a tiny trace of ferromagnetic particles in tissue 
produces a field inhomogeneity and signal loss in MRI images.  
If I remember right, as few as 1000 five nanometer wide magnetite
particles will produce a detectable signal loss in a 1mm wide
voxel of tissue.  From this we can infer that even *ONE* magnetite
containing bacterium would be easily detectable with MRI.  How 
this might be used for brain mapping I will leave to the imagination
of others.
--- Brian Wowk

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