[Gate-users] Number of counts too low

Nicole Jurjew nicole.jurjew at gmail.com
Fri Nov 6 12:32:05 CET 2020

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


/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

/gate/digitizer/Singles/insert timeResolution
/gate/digitizer/Singles/timeResolution/setTimeResolution 0.5 ns

/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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