X-Message-Number: 4800
Date: Mon, 21 Aug 1995 18:43:37 +0200 (MET DST)
From: Eugene Leitl <>
Subject: Re: #4794 (RE: Electron Holography for brain scan)

On Sat, 19 Aug 95 David Stodolsky wrote:

[ electron holography ]
 
> I want to know if there is a physical limit that prevents extraction
> of adequate information. That is, each electron impact will cause
> some damage, but how much damage would be caused by sending an electron
> through each .1 micron voxel? There is no mass heating problem,
> since these electron impacts can be separated by as much time as desired.
> Anybody see an easy way to answer this?

As somebody has already said, there is electron beam 
monochromacy/coherency problem, which all by itself, is quite formidable. 
There is the detector problem: the size, number of pixels. Fortunately, 
electrons are quite easy to detect with CCD-type of detector.

(But one can't wrestle infinite resolution from a finite number of bits: 
the number of electrons we use and the diffraction pattern. I very much 
doubt one can reach even molecular resolution, though this is a guess).

Rad damage: it depends on electron energy. Transmission EMs require thin 
slices, suitably prepared (carbon/platinum, Joe?) and sufficiently high 
energies to penetrate the material. In any case is the energy sufficient 
to break bonds. (Rembember that source of biological rad damage e.g. from 
gamma and xRay comes from secondary electrons).
 
I wit: only thin probes allowed, rad source problems, data acquiry 
problems and accumulating tissue rad damage (bond breakage). I dunno, a 
****ty brew.

Any time we start using any penetrating but interacting radiation, we 
will be getting damage artefacts. The more sharply we look the more the 
damage we cause.

-- Eugene (blame the flu for any stupidity I wrote)


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