[Gate-users] PET scanner NEMA Random coincidences

[Hunor Kertesz]

Dear GATE users,

I am simulating two PET scanners (Siemens mMR and Siemens TPTV). I am 
working on the validation of the systems, following the NEMA NU 2-2012 
protocol, but number of randoms is double when I am plotting the count 
rate.

I am reading the Coincidences (prompts, trues, randoms, scatter), I 
create the sinograms and apply the condition following NEMA ("All pixels 
located farther than 12 cm from the center of the scanner's transaxial 
field of view shall be set to zero"). Then I sum the coincidence 
individually.

For example, if I run a simulation using the scatter phantom (0.001 s, 
just for testing) with 524 MBq I get: 646 trues, 11564 randoms, 440 
scatter coincidences (when reading directly the root file 
(Coincidences)).

In my digitizer I have to coincidence windows:

/gate/digitizer/Coincidences/setWindow 5.86 ns
/gate/digitizer/Coincidences/setOffset 0. ns
/gate/digitizer/Coincidences/MultiplesPolicy takeWinnerOfGoods
/gate/digitizer/Coincidences/describe

/gate/digitizer/name delay
/gate/digitizer/insert coincidenceSorter
/gate/digitizer/delay/setWindow 5.86 ns
/gate/digitizer/delay/setOffset 50. ns
/gate/digitizer/delay/MultiplesPolicy  takeWinnerIfAllAreGoods
/gate/digitizer/delay/describe

I tried multiple configurations, but didn't help, can somebody give me a 
hint on what am I doing wrong or what is the issue?

I experienced the same issue with both models.

I can provide more information regarding my models if needed as well.

Thank you in advance!

Best regards,
Hunor