X-Message-Number: 3362
From:  (David Stodolsky)
Subject: SCI.CRYONICS: Re: Brain Scanning, reply to Yvan Bozzonetti
Date: Fri, 28 Oct 94 09:43:05 +0100 (MET)

In Message: #3360 - Brain Scanning, reply to Yvan Bozzonetti
> From: Brian Wowk <>
> Date: Thu, 27 Oct 94 01:51:28 CDT
> Message-Subject: SCI.CRYONICS Brain Scanning, reply to Yvan Bozzonetti

>the first 1 mm of brain tissue.  To penetrate a 100mm wide brain you  
>will need at least 50keV x-rays, and even then 90% will be absorbed
>before reaching the other side.  >>>> This absorption will occur even

>         There is an even more serious problem with your calculation.
> The number of photons you have estimated is at least 6 orders of
> magnitude too small to make a hologram.  A hologram consists of an  
> interference pattern recorded on a photographic plate or other
> recording medium.  To encode the three dimensional structure of 
> a brain to 0.1 micron resolution, the interference pattern must
> contain 10^18 bits of information.  How are you going to get an
> interference pattern with 10^18 bits of information by recording
> only 10^12 photons?
In an earlier post Yvan writes:

>1 000 eV x 3 x 10^13 photons x 1.6 x 10^-19 joule/eV = 5 x 10^-3 joule or 
>near 0.001 calory or a 10^-6 degre heating of the full 1 kg brain. And this 

If this is right, and we adjust by the 6 orders of magnitude and 50,
then the heating of the brain is "only" 50 degrees.

So, it looks like Yvan is right, that x-ray holography of the brain
can be non-destructive (or at least, not obviously destructive - like
vaporization). (But there may be another factor of ten here, due to
the 90% absorbtion.)

>         Here is yet another problem: How are you going to stop 
> 50keV photons in your detector in a short enough distance to record
> nanometer-scale interference patterns?  Even if you could magically
> stop all 50keV x-ray photons within a nanometer, how would you
> detect only the primary ionization event and distinguish it from
> the shower of secondary scattered electrons (which would spread up

Are there not detectors for physics experiments that use just
this effect?

> to 100 microns away from the initial event).  The only solution
> would be to enlarge the interfernce pattern by moving the recording
> film hundreds of meters away, and using film hundreds of meters wide!

Looks like we are back in space :-)

>         Give it up, Yvan.  Holography with 50keV x-rays is
> psuedoscience!

Might be, but you have not shown a real physical limit, unless the
detector problem can be shown to be limiting in a fundamental way.
And if we only want to take pictures of the cortical sheet, even a
double layer, it might be within range of the current state-of-the-art,
give or take $6 billion or so.


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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