MRI and dino eggs, etc.

[murdoch@mr.picker.com (Jim Murdoch)]

With regard to the use of magnetic resonance imaging (MRI)
in the study of dinosaur eggs ...

It HAS been investigated, notably by Neil Clark (a frequent 
contributor to this forum) and co-workers from Glasgow.  They
report that "the images show a shell structure distinct from
the rest of the egg.  By acquiring a projection of the entire
egg, the water content of the shell was measured ...." (M.
McJury, N.D.L. Clark, J. Liston, and B. Condon, Proceedings
of the Society of Magnetic Resonance, Second Meeting, August,
1994, p. 706).

These results reflect a major limitation of conventional MRI:
only comparatively mobile hydrogen nuclei can be detected, such
as those from soft tissue, lipids, various bodily fluids ...
and adsorbed water on or in egg shells.  (The same mobility limitation
applies when other MR-active nuclei, such as phosphorus-31 and
carbon-13, are examined.  In the absence of motion, the little
nuclear magnets interact with each other, completely washing out the
spatial encoding necessary for imaging.  A more painful and
protracted explanation can be provided, if so desired ....)

A more thoroughly pursued and successful "geo-application" of MRI is
the analysis of oil well cores.  What is imaged is the liquid-like
oil and/or water in the sandstone pores.  The images provide 
information about oil/water distribution, efficiency of enhanced oil 
recovery, diffusion rates, pore size and connectivity, etc.  Therefore,
by analogy, perhaps some fossils in certain matrices could be MR imaged
by the presence or absence of pore fluids.  The content of
paramagnetic ions (such as iron) must be low, however -- otherwise, 
the unpaired electrons mess things up.

Finally, it IS possible to image some rigid solids (such as P-31
in bone) directly, but at present, these are difficult experiments on
very small samples.

Now back to dinos ....

Jim Murdoch
Picker International (a medical imaging company -- surprise, surprise)
Highland Heights, Ohio