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

Mon Aug 27 19:00:26 CEST 2007

Hi Andrew,

I don't really understand this answer.  We have found a different  
pattern concerning the ordering in the coincidence output.  Maybe the  
code has changed.  From looking at time difference spectra for a  
given detector pair (i.e. time of det b minus time of det a, _not_  
time of column 2 minus time of column 1) it appears that true and  
random coincidences are treated differently.  For trues, it seems  
that the order can be either way (don't know what determines the  
order) but for randoms, the 2nd single is always the later one.   
Given this, it is still disconcerting to me that the energy spectra  
are different.  True and random coincidences can have different  
energy spectra (due to different constraints on geometry) but I don't  
see how this could explain your effect.   Hopefully if you sort by  
detector or detector pair instead of the position of the data in the  
file, the energy and time spectra would make sense.

Paul

Paul Vaska, Ph.D.
Medical Department, Building 490
Brookhaven National Laboratory
Upton, NY 11973
vaska at bnl.gov (631)344-6228 fax:(631)344-4146

On Aug 27, 2007, at 11:09 AM, yuxuan.zhang at di.mdacc.tmc.edu wrote:

>
> Hi,
>
> This effect is not something new. One or two years ago someone  
> already found this and reported here.
> At that time I was also curious about this so I spent some time  
> looking into it. After reading the source
> code, my conclusion is that this result is caused by the GATE code  
> about how it processing the energy
> deposit from hits.
>
> When two gamma ray photons travel inside the material, GATE records  
> all the energy deposit in an array.
> Then in the "adder" process, GATE will add up all the energy  
> deposits from the same gamma photon and
> stored in one of the cells in the same array. During this step, the  
> gamma photon with a higher total deposited
> energy will always stored in front of the other gamma photon (or  
> after, I can remember clearly). So in
> the output file the photon1 and photon2 are just a label, it does  
> not represents the original photon1 or
> photon2.
>
> So if you really want the spectrum of the coincidences, just add  
> the photon1 and photon2 together.
>
> Yuxuan
>
>
>
>
> Irène Buvat <buvat at imed.jussieu.fr>
> Sent by: gate-users-bounces at lists.healthgrid.org
> 08/26/2007 09:19 AM
>
>
>         To:        gate-users at lists.healthgrid.org
>         cc:
>         Subject:        [Gate-users] Fwd: FW: Difference in energy  
> spectrum for first and second event in         cylindrical PET system
>
>
>
> X-Ids: 165
> X-Greylist: delayed 857 seconds by postgrey-1.21 at ns2919.ovh.net;
>   Sat, 25 Aug 2007 00:17:05 CEST
> X-IronPort-AV: E=Sophos;i="4.19,305,1183352400";
>  d="mac'?jpg'145?scan'145,208,217,145";a="310266"
> 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>
> X-OriginalArrivalTime: 24 Aug 2007 21:54:28.0267 (UTC)
>        FILETIME=[57E9BFB0:01C7E699]
> Sender: mailman-bounces at lists.healthgrid.org
> X-Virus-Scanned: ClamAV 0.88.7/4054/Fri Aug 24 18:55:59 2007 on  
> shiva.jussieu.fr
> X-Virus-Status: Clean
> X-Miltered: at shiva.jussieu.fr with ID 46CF5710.007 by Joe's j- 
> chkmail (http://j-chkmail.ensmp.fr)!
> The following message was rejected by the address 'gate- 
> users at lists.healthgrid.org'.  Could you please post it on my behalf?
> 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>>
>
> Content-Type: image/jpeg;
>       name="EnergyHistogram.jpg"
> Content-Description: EnergyHistogram.jpg
> Content-Disposition: attachment;
>      filename="EnergyHistogram.jpg"
>
>
> Content-Type: application/octet-stream;
>   name="microPETR4.mac"
> Content-Description: microPETR4.mac
> Content-Disposition: attachment;
>        filename="microPETR4.mac"
>
>
> This email and/or any documents in this transmission is intended  
> for the
> addressee(s) only and may contain legally privileged or  
> confidential information.  Any unauthorized use, disclosure,  
> distribution, copying or dissemination is strictly prohibited.  If  
> you receive this transmission in error, please notify the sender  
> immediately and return the original.
>
> Ce courriel et tout document dans cette transmission est destiné à  
> la personne ou aux personnes à qui il est adressé. Il peut contenir  
> des informations privilégiées ou confidentielles. Toute  
> utilisation, divulgation, distribution, copie, ou diffusion non  
> autorisée est strictement défendue. Si vous n'êtes pas le  
> destinataire de ce message, veuillez en informer l'expéditeur  
> immédiatement et lui remettre l'original.
>
>
> -- 
>
> 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_______________________________________________
> Gate-users mailing list
> Gate-users at lists.healthgrid.org
> http://lists.healthgrid.org/mailman/listinfo/gate-users
>
>
> _______________________________________________
> Gate-users mailing list
> Gate-users at lists.healthgrid.org
> http://lists.healthgrid.org/mailman/listinfo/gate-users