[gate-users] random coincidence

[Claude Comtat]

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
> 
> 
> 
> 
> 
> 
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> 


-- 
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