[Gate-users] Fwd: FW: Difference in energy spectrum for first and second event in cylindrical PET system

[Irène Buvat]

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>Subject: FW: Difference in energy spectrum for first and second event in
>	cylindrical PET system
>Date: Fri, 24 Aug 2007 16:54:28 -0500
>Thread-Topic: Difference in energy spectrum for first and second event in
>	cylindrical PET system
>Thread-Index: Acfmlfu0s1jG3B4WQ1WCyGHMNxLkBQAAzp2w
>From: "Andrew Goertzen" <AGoertzen2 at exchange.hsc.mb.ca>
>To: <gate-users-owner at lists.healthgrid.org>
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>Thanks,
>Andrew
>
>
>Hi All,
>
>I am simulating a cylindrical PET system in GATE 3.0.0 with the 
>geometry of a microPET R4 and I am hoping someone can help explain 
>the behaviour I am seeing.  My source is a 1.25 MBq line source at 
>the centre of the FOV.  Data is written to an ASCII text file.  When 
>I create an energy histogram from the coincidence data output file I 
>notice that the events identified as 'single 1' in a coincidence 
>event (i.e. columns 1-21 of a coincident event in ascii format as 
>described in section 10.1 of the user manual) have a different 
>energy spectrum than events identified as 'single 2'.  I have 
>included an example of this in the attached jpg image.  I do not 
>think it is time related because I get this behaviour with and 
>without 1.5ns of time blurring.  Also, the timestamp for single 1 is 
>not always less than for single 2.  I do not think it is energy 
>related because the energy of single 1 is neither always greater 
>than or always less than single 2.
>
>So I am hoping that someone can answer the following questions:
>How does GATE determine the order of singles that make up a coincident event?
>Has anyone else observed this sort of difference between the first 
>and second single?
>
>I have included the .mac file I am using.
>
>Regards,
>Andrew Goertzen
>Department of Radiology
>University of Manitoba
>
><<EnergyHistogram.jpg>> <<microPETR4.mac>>
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-- 
Irene Buvat, PhD
Equipe "Imagerie de la perfusion et des échanges moléculaires"
U678 INSERM
CHU Pitié Salpêtrière
91 Boulevard de l'Hôpital
75634 Paris Cedex 13
France
Tel : 01 53 82 84 19
Fax : 01 53 82 84 48
email : buvat at imed.jussieu.fr
http://www.guillemet.org/irene
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