X-Message-Number: 4873
Newsgroups: sci.cryonics
Date: Wed, 13 Sep 1995 21:46:20 +0200 (MET DST)
From: Eugene Leitl <>
Subject: neurotissue voxel imaging at molecular resolution
Message-Id: <>

High-resolution (till down to molecular level) 3d scan of cerebral 
tissue is a long-pursued dream of neuroscience.

With relatively recent advent of vitrification and ultrarapid 
freeze of biotissue specimens at least the long-term stability 
of "tissue snapshot" has been assured. However, how can a small 
tissue block be transformed into the according voxel block?

Water ice sublimates if exposed to hard vacuum. Vacuum etching of
cytosol and a subsequent carbon/platinum shading is a widely used
EM contrasting technique. Though high glycerol (and other polyols) 
levels will reduce cytosol sublimation rate, phospholipid membranes 
and cytosol embedded proteins remain prominent, however. 

What to do?

A complementary abrasion technique can be the UV (excimer) etching. 
Short hard UV laser pulses virtually turn a few-nm thin surface layer
into an ionized, rapidly expanding gas cloud which get rapidly pumped
off by the turbovac (surface must be clean, hence no oildiff (at least
without a cryotrap baffle)).

The fine details of the exposed (both (cycled) vacuum etch and excimer
pulse) surface can be scanned by an AFM (atomic force microscope) at
relatively high (audio to video) bitstream rate. UV photoionisation
potential background induced problems do not appear unsurmountable.
E.g. cryovitrified synapse 3d scan at molecular resolution might be
attainable with above abrasive microscopy technique. Since ultrarapid
freezing can snapshot few-ms processes this method might feature both
high temporal and spatial resolution.

The experimental setup would require a small (fist-sized) vacuum 
chamber with vacuum-tight electrode array, a turbovac (vibration!) 
or a cryotrap-baffle equipped oildiff, a standard vacuum-proof AFM 
with an attached computer, a weak pulse excimer laser, a fiber or 
window UV-clear optics, a copper finger cooled with an appropriate 
solvent sludge as tissue base and a low-vibration workbench. Extensive 
earthing might be needed due to UV-induced photopotentials. Discontinous 
use (vacuum cycling) appears straightforward.

Though above equipment list may appear formidable, it can be easily
allocated at any well-funded university. Since this is only proof of 
principle (POP), all gadgets can be recycled after few month's duration.

-- Eugene

P.S. Joe Strout, the founder of NEL, arrived at the same method 
     independantly.


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