[gate-users] Re: random coincidence

[Qianmei Zhang]

Thanks Claude,
 
You are right, and i now understand.

To prove it, I added the line 
/gate/digitizer/Coincidences/minSectorDifference  22 and got the same 
number. The reason is that the radial cut would have no effect if the 
line was inserted in.

Best wishes

Qianmei



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>Message: 2
>Date: Fri, 28 Jan 2005 09:53:23 +0100
>From: Claude Comtat <comtat at ieee.org>
>Subject: Re: [gate-users] random coincidence
>To: GATE feedback and helpline for Users
>	<gate-users at lphe1pet1.epfl.ch>
>Message-ID: <41F9FD83.2040002 at ieee.org>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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>I don't know if this is the explanation, but there is not only a 
>geometrical cut in /gate/output/sinogram on the ring difference, but 
>also on the radial coordinate of the LOR.
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>/gate/output/sinogram/RadialBins 256
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>If you use a root program and want to compare it to the sinogram output, 
>you should also apply this radial cut (for more details, see user's 
>guide, section data output / sinogram output).
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>Regards,
>
>Claude
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>Qianmei Zhang wrote:
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>>Hello Gater User,
>>
>>I met a puzzle about the random coincidence.
>>
>>In order to model the effect from random coincidnence for a Ecat 953 
>>system (16 rings), i run two cases, one without and the other with the 
>>flag:/gate/output/sinogram/TruesOnly , and i got two Ecat7 output files, 
>>by the intergral of counts of the subtraction of the two file, the total 
>>random number was obtained.  Since the maximum ring difference i set is 
>>13, the number should be a little bit of smaller than the actual random 
>>coincidence number.
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>>I also modified the C program in the benchmark and by run it with the 
>>root output file from the first case, i can obtain the number of  random 
>>as well (if the two eventIDs in coincidence are different, they  belong 
>>to random coincidnence )
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>>For  the same  decay of  the source, in a very short run, from the first 
>>method, the number i got is 272, after corrected by the effect from the 
>>ring difference, it will be 356.  and the number from the second method 
>>is 500.  The difference is out of statistical uncertainty. I also run it 
>>for a longer time, but it seems same.  By the way, for this case, the 
>>deadtime is 3000ns and coincidence window is 12ns and the source 
>>activity is 0.8mCi.
>>
>>Can anyone here explain it for me, thanks.
>>
>>Qianmei
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