[Gate-users] Number of counts too low

[Maxime Toussaint]

Greetings,

I am not aware of publicly available NEMA NEC validation with GATE. Your problem is a disparity between number of gamma pair detected vs kept, right? If you start from a known example, e.g. the benchPET configuration and apply your test from there, you might get some idea/intuition. It can be a long process but it is the best I can suggest.

Bests,
Maxime Toussaint
________________________________
De : nicole.jurjew at gmail.com <nicole.jurjew at gmail.com>
Envoyé : 10 novembre 2020 10:57
À : Maxime Toussaint <Maxime.Toussaint at USherbrooke.ca>; gate-users at lists.opengatecollaboration.org <gate-users at lists.opengatecollaboration.org>
Objet : AW: [Gate-users] Number of counts too low


Dear Maxime,



once again, thank you for your reply. Of course I understand that you won’t read a full set of mac files. Nevertheless, I haven’t found a publication yet with reproducible GATE – settings for a validated model, let alone a validated model which is available online. Do you know of a GATE model which was validated with the NEMA NEC measurements you can point me to?



Thank you in advance,

Kind regards,

Nicole



Von: Gate-users <gate-users-bounces at lists.opengatecollaboration.org> Im Auftrag von Maxime Toussaint
Gesendet: Dienstag, 10. November 2020 16:46
An: gate-users at lists.opengatecollaboration.org
Betreff: Re: [Gate-users] Number of counts too low



Greetings,



In short, I don't know. It could be too many thing since I am missing a great portion of your simulation configuration. As it stand, I am not even sure if the problem is in the choice of digitizer.



Most, including I, won't take the time to analyze/read a complete list of mac files. Thus, I suggest that you start from one of Gate example, which we know should work, and slowly replace it with your simulation configuration (Or do the reverse). This way, you will be able to "find" the part, 3-4 lines, from where the problem is born.



Good luck in your hunt!



Bests,

Maxime Toussaint



________________________________

De : nicole.jurjew at gmail.com<mailto:nicole.jurjew at gmail.com> <nicole.jurjew at gmail.com<mailto:nicole.jurjew at gmail.com>>
Envoyé : 10 novembre 2020 05:47
À : Maxime Toussaint <Maxime.Toussaint at USherbrooke.ca<mailto:Maxime.Toussaint at USherbrooke.ca>>; gate-users at lists.opengatecollaboration.org<mailto:gate-users at lists.opengatecollaboration.org> <gate-users at lists.opengatecollaboration.org<mailto:gate-users at lists.opengatecollaboration.org>>
Objet : AW: [Gate-users] Number of counts too low



Dear Maxime,



thank you for your reply!



I tried your suggestions out: The DTVolume level changes the number of counts a little, but by far not significantly (about 0.5% more counts where I need around 50% more for low energies). I also ran with the most simple digitizer: no energy blurring, no time resolution or dead time added. I get the same results: about 0.5 % increase of counts, but no significant changes.



Do you maybe have any other ideas why I get too little counts?



Thank you!

Kind regards,

Nicole



Von: Gate-users <gate-users-bounces at lists.opengatecollaboration.org<mailto:gate-users-bounces at lists.opengatecollaboration.org>> Im Auftrag von Maxime Toussaint
Gesendet: Dienstag, 10. November 2020 05:18
An: gate-users at lists.opengatecollaboration.org<mailto:gate-users at lists.opengatecollaboration.org>
Betreff: Re: [Gate-users] Number of counts too low



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<mailto:gate-users-bounces at lists.opengatecollaboration.org>> de la part de Nicole Jurjew <nicole.jurjew at gmail.com<mailto:nicole.jurjew at gmail.com>>
Envoyé : 6 novembre 2020 06:32
À : gate-users at lists.opengatecollaboration.org<mailto:gate-users at lists.opengatecollaboration.org> <gate-users at lists.opengatecollaboration.org<mailto: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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