X-Message-Number: 4764
Date: Fri, 11 Aug 1995 09:55:27 -0700 (PDT)
From: Joseph Strout <>
Subject: Re: electron holography

Electron holography can be accomplished in a variety of ways, and this 
has been done with some success.  However, it's not that much different 
from conventional transmission electron microscopy; you have the same 
problems of sample thickness and cooking.  Theoretical treatments of 
electron holography generally assume a sample thickness of about 5 nm or 
less.  More elaborate theory can work with thicker samples, but you run 
into a real practical limitation due to electron scattering: as the 
thickness increases, electrons start colliding and end up going every 
which way, producing useless noise.  As the thickness increases, the 
signal-to-noise ratio drops.

When it works, e. holography has improved the resolution by a factor of 
about 1.5 as compared to convential imaging.  Most of the really exciting 
applications of this technique have been in imaging magnetic fields on a 
very fine scale (e.g., even individual "flux quanta" in a 
superconductor).

So, while it's a neat technology and useful for a lot of things, to use 
it for a brain recording would still requiring slicing your brain very 
thin and then cooking it.

Much of the above info, plus a good mathematical treatment, can be found 
in a review article: Cowley, J.M., "Twenty forms of electron holography" 
Ultramicroscopy 41: 335-348 (1992).

,------------------------------------------------------------------.
|    Joseph J. Strout           Department of Neuroscience, UCSD   |
|               http://sdcc3.ucsd.edu/~jstrout/    |
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