[gate-users] random coincidence

[Qianmei Zhang]

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