[gate-users] Re: gate-users Digest, Vol 10, Issue 26

[Long ZHANG]

Sorry for the trash :-( 

In your mail:
>From:Long Zhang <mr.long.zhang at gmail.com>
>Reply-To: Long Zhang <mr.long.zhang at gmail.com>,
  GATE feedback and helpline for
Users <gate-users at lphe1pet1.epfl.ch>
>To: gate-users at lphe1pet1.epfl.ch
>Subject: [gate-users] Re: gate-users Digest, Vol 10, Issue 26
>
>Dear Claude,
>
>You are right. The difference is due to the geometrical cuts when GATE
>build sinograms from coincidence events for ECAT system.
>
>However, my suggestion is to directly remove those cuts. e.g. by using
>/gate/output/sinogram/RadialBins N_crystals/ring-1
>and do not use the max ring difference parameters when generating the
>sinogram or set it to number of rings -1. Thus the sinogram will use
>all events.
>
>Another question is the two runs. The random numbers generation is
>based on a seed file. So if this file is the same, the two runs will
>be the same except one with TruesOnly flag on. So there is no
>statistical problems.
>
>Hope this helps.
>
>Regards,
>
>Long
>
>
>> 
>> 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.
>> 
>> /gate/output/sinogram/RadialBins 256
>> 
>> 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).
>> 
>> Regards,
>> 
>> Claude
>> 
>> Qianmei Zhang wrote:
>> 
>> >
>> > 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.
>> >
>> > 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 )
>> >
>> > 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
>> >
>> >
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > gate-users mailing list
>> > gate-users at lphe1pet1.epfl.ch
>> > http://lphe1pet1.epfl.ch/mailman/listinfo/gate-users
>> >
>> >
>> 
>> --
>> Claude Comtat                                   comtat at ieee.org
>> Image Acquisition and Processing group          tel: +33 1 69 86 78 01
>> Frédéric Joliot Hospital Facility               fax: +33 1 69 86 77 49
>> French Atomic Energy Commission                 www-dsv.cea.fr/shfj
>>
>
>_______________________________________________
>gate-users mailing list
>gate-users at lphe1pet1.epfl.ch
>http://lphe1pet1.epfl.ch/mailman/listinfo/gate-users
>