X-Message-Number: 5135
From:  (Brian Wowk)
Newsgroups: sci.cryonics
Subject: Re: Beyond 2000 and Mind Uploading
Date: 6 Nov 95 17:53:08 GMT
Message-ID: <>

References: <> 
<47jb0l$>


In <47jb0l$>  (David L Evens) 
writes:

>My understanding is that field strength changes are performed by the use 
>of radio waves.  (I have used a NM spectrometer that used a powerful 
>permanent magnet for producing the field, and the principle difference 
>between MNS and MRI is the method of data extraction and processing.)

	The field strength changes needed for MRI are produced by
low-frequency current pulses in gradient coils.  The nuclei to be
observed are excited by a separate rf coil that produces radio-freqency
magnetic oscillations.  Radio waves are not used in MRI or MRS.

>The effectiveness of the instrument is measured both in terms of magnetic 
>field strength, which is intended to be highly uniformly produced by the 
>magnetic coils, and the intensity and precision of the radio wave pulse 
>used to activate the nuclei that are to be sampled.  My impression at the 
>time was that the higher an RF frequency was used, the cleaner the data 
>would be, but the stronger the field required was.

	Substitute "radio wave pulse" with "rf pulse", and this paragraph
is essentially correct.


>There might be some problems with the energy input to the brain while the 
>field is established or the brain inserted, but it should be possible to 
>image with a relatively low flux of energy available for absorbtion by 
>the brain, if enough time is taken in the imaging process.  Certainly, a 
>frozen brain is going to be arround for as long as you care to take, so 
>extremely low flux rates can be used to get the data without damaging the 
>brain.

	The rate at which you can extract data with MR is inherently
limited by the T1 relaxation time of the sample, which actually increases
with field strength.  It is also extremely difficult (i.e. tedious)
to do MR on solids like ice because the signal persists for only  
microseconds after each excitation (extremely short T2). 

	What really kills you, though, is the infamous 6th power
relation between scan time and resolution (at constant SNR) that
exists in MRI.  If you could scan an entire brain with 1mm resolution
in 1 second, it would take you 10^28 years to scan that brain with
1 nanometer resolution.  Even I don't believe that patients can be
kept frozen for that long (or that they would WANT to be frozen that
long!:) 

	X-ray CT scanning can be ruled out for similar reasons.  The
bottom line is that it is not possible within the bounds of known
physical law to non-invasively obtain the detailed neural information
needed for uploading.  In-situ nanotechnology is essential.  (None of
this precludes the possibility that someday people will redesign 
their brains so that rapid data readout is possible, but that again
requires advanced NT.)   

---Brian Wowk


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