[gate-users] Energy Spectrum Woes - Dual Head and 4 Head Designs

[Sophie Kerhoas]

Bonjour Angela,
   You are right, your energy spectra are strange....Is it possible to
have your macro files (geometry, source and digitizer) in order to track
the bug.
 Have a good day,
Sophie

--------------------------------------
Sophie Kerhoas-Cavata
Service de Physique Nucleaire,
CEA/DSM/DAPNIA/SPHN
91 191 Saclay

On Thu, 2004-09-02 at 04:40, Angela M K Foudray wrote:
> Recently my labmates and I have been looking into two head and 4 head 
> PET system designs using LSO crystals for scintillators, F18 in water
> phantoms for the source+phantom... I can give you more details if you
> like... but we have been increasingly alarmed over the energy spectra
> that we have been getting.  We have been looking at the energies output
> in the Coincidence file of the two photons seperately.  We have been
> getting very confounding results.  First off, the two spectra are not
> "the same" (and of course, I don't mean small differences you're going
> to get from Monte Carlo) - they're just not similar.  There is a high
> energy peak near 700 keV and a low energy peak near 200 in one of them
> that we can't explain, and there's a compton peak near 350 keV in only
> the one that doesn't have the strange 200 keV peak.  If there was a
> weird 700 keV peak and a weird 200 keV peak in *both* of them, I would
> be slightly less worried - maybe - but the spectra just are completely
> different.  I understand that "photon one" (the first one listed in the
> coincidences file) is simply the first photon of a pair that, with a
> particular time resolution, happened to be "detected" first - with a
> great number of counts, the spectrum from photon one should be, to the
> eye, nearly exactly the same as the energy spectrum for photon two,
> statistically.  
> 
> I have attached a picture of the two energy spectra for a particular
> simulation (they *always* come out the same, the spectrum for photon one
> has a weird low energy peak and small compton peak, as well as a weird
> high energy peak) displaying the current bane of our simulations.
> 
> What is going on?
> 
> If you have *ANY* insight... hit me with it!
> 
> Ange
> 
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