X-Message-Number: 3344
From: Brian Wowk <>
Date: Mon, 24 Oct 94 00:27:41 CDT
Subject: SCI.CRYONICS Brain scanning, reply to Yvan Bozzonetti

Yvan Bozzonetti:
> I fear B. Wowk mix anything, first, QED is the general theory of 
> electromagnetism and is never used for computing complex situations. 
        Are you suggesting that QED is not used in the real world?
On the contrary, QED is *the* theory that predicts how photons such 
as x-rays interact with electrons in matter!  X-ray interactions of 
great biological importance (such as electron-positron pair production 
during clinical radiotherapy) cannot be understood without QED.  
Even the Klein-Nishina differential cross sections for Compton 
scattering require relativistic quantum mechanics (the precursor to 
full QED) for their derivation.  
        In any case, I do not want to engage in a history lesson
on radiation transport theory.  The important point is this: 
The mechanisms by which x-rays interact with matter are exactly
and quantitatively understood in both theory and experiment to
many decimal places.
> Second, Bragg scattering in about diffraction by a crystal network of 
> atoms, the monochrmaticity produced by that system is similar to the one 
> generated by a prism in visible light. This far from what a hologram needs. 
> So the subjects are not the same.
        Indeed, the subjects are not the same.  I was not talking about
holography when I referred to Bragg scattering.  I was responding to
your assertion that my knowledge of x-ray interactions was based
on experiments with polychromatic beams.   
> There may be an understanding problem: May be I have not sufficiently 
> stressed than Xray brain scanning was essentially a cryonics tool. That is, 
> it must be used at low temperature when the brain is a solid body. There, I 
> am sorry, but you cannot take as model the atomic properties of a gas or a 
> liquid. Not only atoms are locked in molecules (mostly big ones for 
> interesting cases) but they are anchored in the solid. Recall the Mosbauher 
> effect, where an entire crystal absorbs the push of a single photon. Even 
> at atom border electrons are not knocked out in a solid as in a gas.
        No.  This is not correct!  Chemical binding only affects the 
energy levels of valence electrons by a few electron volts.  This is   
not going to have any effect on interactions with keV x-rays.  Also, 
the Mossbauer effect is a *nuclear* effect, and does not occur with
electrons.  In summary: whether a brain is liquid or frozen is not  
going to have any dramatic effect on its x-ray dosimetry.
        Yvan, normally I don't make arguments from authority, but
because this argument is becoming tedious I'm now going to.  I have
a Master's degree in medical physics (soon Ph.D.), which makes me an
expert in medical imaging and the biological effects of ionizing
radiation.  I am telling you that nanometer-scale resolution of
intact brains (frozen or unfrozen) by any form x-ray imaging is 
not practical because of the large energy deposition that would  
result.  To argue otherwise you must
a)  Provide an estimate of the number of x-ray quanta of a certain
    energy that must pass through the brain to provide an image 
    of such resolution.
b)  Provide a calculation (using a formula from the literature)
    showing that the fraction of quanta which deposit energy 
    in the brain is small enough to cause minimal heating.
--- Brian Wowk

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