[Gate-users] Number of counts too low

[Maxime Toussaint]

Greetings,

I have never used the deadtime module, but are you sure about your choice for the following?
"""
/gate/digitizer/Singles/deadtime/chooseDTVolume rsector
"""
It seems to be to "low" in "geometry level" for classical scanner configuration.

If yes, did you try to simplify (e.g. remove dead time) of your digitizer to find the origin of the problem?

Bests,
Maxime Toussaint

________________________________
De : Gate-users <gate-users-bounces at lists.opengatecollaboration.org> de la part de Nicole Jurjew <nicole.jurjew at gmail.com>
Envoyé : 6 novembre 2020 06:32
À : gate-users at lists.opengatecollaboration.org <gate-users at lists.opengatecollaboration.org>
Objet : [Gate-users] Number of counts too low

Dear Gate Users!

I am using GATE v.8.0 to model a preclinical PET system. I carried out the NEMA - NEC measurements on the real scanner and also simulated them in GATE. The curves don't look much alike. The simulation produces significantly less counts than what is detected with the real system.

I determined the number of gamma particles entering my crystal with the "Kill Tracks" Actor. (I always ran one simulation to count the Nb of tracks killed in the crystal and one where no tracks are killed to be able to calculate the Nb of prompts generated.)

An activity of 0.58 MBq inside a polyethylene cylinder results in a total number of ~21.000 counts with the digitizer settings you can see below. Number of killed gamma particles is ~855000.
Energy window, coincidence timing window and dead time are set to align  with specifications given by the vendor. I tried out many different digitizer settings, but none of them leads to a result close to the measurements, also not for higher activities up to 40 MBq.


Do you have an idea where too little counts could come from?


Thank you in advance!
Nicole Jurjew




### DIGITIZER ###

/gate/digitizer/Singles/insert adder
/gate/digitizer/Singles/insert readout
/gate/digitizer/Singles/readout/setPolicy TakeEnergyWinner
/gate/digitizer/Singles/readout/setDepth 1

/gate/digitizer/Singles/insert blurring
/gate/digitizer/Singles/blurring/setResolution 0.1
/gate/digitizer/Singles/blurring/setEnergyOfReference 511. keV

/gate/digitizer/Singles/insert thresholder
/gate/digitizer/Singles/thresholder/setThreshold 250.39 keV
/gate/digitizer/Singles/insert upholder
/gate/digitizer/Singles/upholder/setUphold 771.61 keV


# C O I N C I    S O R T E R
/gate/digitizer/Coincidences/setWindow 7. ns
/gate/digitizer/Coincidences/MultiplesPolicy  takeWinnerOfGoods

/gate/digitizer/name                            delay
/gate/digitizer/insert                          coincidenceSorter
/gate/digitizer/delay/setWindow                 7. ns
/gate/digitizer/delay/setOffset                 20 ns


# TIME RESOLUTION
/gate/digitizer/Singles/insert timeResolution
/gate/digitizer/Singles/timeResolution/setTimeResolution 0.5 ns


#   DEAD TIME
/gate/digitizer/Singles/insert deadtime
/gate/digitizer/Singles/deadtime/setDeadTime 850. ns
/gate/digitizer/Singles/deadtime/setMode nonparalysable
/gate/digitizer/Singles/deadtime/chooseDTVolume rsector
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