X-Message-Number: 729
Date: 13 Apr 92 03:09:17 EDT
From: Brian Wowk <>
Subject: fixation and hi-res scanning

To: >INTERNET: 
 
        I'd like to expand a bit on comments made by Thomas Donaldson in  
response to Richard Fleischer's questions about chemical fixation and high  
resolution brain scanning. 
 
        When tissue is frozen by slow cooling there is a tendency for cells  
to dehydrate by osmosis (ice forming outside cells creates a hypertonic  
solution).  This dehydration is generally beneficial; it's less damaging for  
water to freeze outside a cell than in it. 
 
        Regarding this phenomenon, Dr. Gregory Fahy reported at Alcor's  
recent anniversary dinner that chemical fixation renders normally semi- 
permeable cell membranes impermeable, preventing cellular dehydration during  

cooling.  This results in the formation of highly-damaging intracellular ice.
Chemical fixation procedures such as embalming are therefore not appropriate  
for a cryonic suspension protocol. 
 
        I'm not sure whether this information was available when Drexler  
wrote Engines of Creation.  There may have been good arguments around at that  
time in support of fixation before vitrification (or freezing).  The  
important points to realize are that any technique involving storage below  
-130'C (the temperature at which even unfrozen water becomes rock solid) will  
be sufficient for "long-term biostasis", and that no such techniques are  
currently reversible at an organ level. 
 
        Because we don't yet have nanotechnology to recover preserved organs,  
it's very difficult optimize preservation protocols.  (What criteria does one  
use to judge preservation quality?)  As Drexler points out in his book,  
cryonicists have traditionally taken the conservative approach of preserving  
tissue function as best as possible.  (We know, for example, that at least  
the individual cells of our suspension patients are still viable.)  Hindsight  
now reveals the wisdom of this approach.  It will likely continue in the  
future as we push toward demonstrably reversible brain preservation  
protocols. 
 
        On the subject of high resolution brain scanning, I don't think CT  
scanning will ever be practical for this application.  The radiation dose  
deposited in tissue scales as the sixth (yes, I said 6th) power of CT scanner  
resolution.  For scanning at the cellular scale, the radiation damage would  
be prohibitively large. 
 
        Interestingly, no such restrictions exist for MRI.  If the formidable  
engineering obstacles can be overcome, MRI in conjunction with Thomas  
Donaldson's nanorobotic imaging probes may well be the brain and memory  
recording tools of the future. 
 
                                                --- Brian Wowk 

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