X-Message-Number: 3308
From:  (David Stodolsky)
Subject: SCI.CRYONICS: Brain holograms
Date: Thu, 20 Oct 94 12:13:43 +0100 (MET)

Jacobsen, C., Howells, M., Rothman, S, & Bastacky, J. (Aug. 1989).
X-ray holography: Early experience in microimaging.
In _X-Ray Microimaging for the Life Sciences. 
Proceedings of the Workshop May 24-26, 1989._ (pp. 69-73)
Berkeley, CA: Lawrence Berkeley Laboratory, U. of Calif. 

"Images ... have indicated that our current techniques gives a system
resolution of 600 Angstroms or better....

The attractions of holography as a soft x-ray imaging technique include
the simplicity of the x-ray optics (only a monochromator plus pinhole
is required), the ability to make use of single-shot x-ray sources
(such as x-ray lasers) when they become available at the required
wavelength and brightness, the natural way in which phase contrast
can be used in holographic imaging, the fact that the focussing of
the image is accomplished in the reconstruction stage (_without_
additional exposure of the specimen to x-rays), and the possibility
of extension to diffraction tomography for achieving high-resolution,
three-dimensional images." (p. 70).


My brother's comments 
(He is working in the Office of Health and Environmental Research,
U. S. Dept. of Energy, on the Human Genome project):


This research line was discontinued because if became evident that
the resolution needed for DNA sequencing could not be achieved.

DOE/OHER looked into the possibilities of X-ray holography,
had a conference etc.
Main tech problems are:
1. The only X-ray sources approaching coherence have very narrow beams.
2. You would have only one shot and the sample would be fried. Remember,
   X-rays ionize.
3. Only thin specimens would be suitable.
4. For holography the initial beam must be split into a Reference and
   Target beam which must be rejoined on the detectors -
   this is non-trivial!

There are, however, some good folks working on constituents of the problem.



David S. Stodolsky, PhD               Internet: 
Peder Lykkes Vej 8, 4. tv.      (C)         Tel.: + 45 32 97 66 74
DK-2300 Copenhagen S, Denmark                Fax: + 45 32 84 08 28

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