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Article #651

Getting more out of PET and fMRI!

#651
From: Stephen Hicks
Date: Sun, 17 May 1998 00:00
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I can suggest an area that definately needs some mathematical help.
Interpreting the PET and fMRI images of humans "in thought".  The method
commonly used is merely subtracting the highest changes in energy from a
baseline taken previously.  This is a misleading technique that presents
the researcher with those famous "Modes of Cognition" pictures that
frequently cover psychological journals.  You could explore better ways
to extract information from these images rather then using the feeble
"Subtraction Technique".

For example:  The temporal resolution for PET is around 40 seconds as
positrons must be given time to accumulate in the sensors. So assuming
that during that time the neurons under that "bright spot" were
continuously "on" is a misinterpretation.  The region may have lit up
very brightly only for a second, or it may have flickered intermediately
throughout the 40 secs, or indeed any permutation of the two factors,
length of time, and energy released.

The variables-
-The amount of radiation collected. (read off the scan)
-The energy output of the neurons in that specific region. (easy if they
are just cortical neurons, calculate their density,  plus their
individual power needs  (rem: most PET measure only change in blood
flow!) )
-The amount of time elapsed during the scan.

You should be able to get a better idea about what the region was doing
during that time,  eg. how long it was on and how long it was off, would
tell you the frequency of those neurons.
At any rate it would be far more informative then what we presently do!
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From: Stephen Hicks <oleosat@bigfoot.com>
Subject: Getting more out of PET and fMRI!
Date: 1998/05/17
Message-ID: <355DB2C2.8DA3BBC6@bigfoot.com>
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