[Gate-users] problematic behavior of deadtime in PET detector
Julien Salvadori
j.salvadori89 at gmail.com
Thu May 14 23:06:51 CEST 2020
Hi Zhhengzhi,
You perform the integration and apply the dead time at the highest level of
the system (at the crystal level). The higher the dead time is modeled in
the geometry, the lower the count loss is for a given dead time. At first
glance, your results don't seem so inconsistent to me.
Why do you want to model the dead time at the crystal level ? Have you
tried to model the dead time at a lower level in your geometry (the modules
for example) ?
Best
Julien Salvadori
Le jeu. 14 mai 2020 à 23:44, Zhengzhi Liu <zliu36 at stanford.edu> a écrit :
> Honored Gate experts and developers,
>
> I am experiencing some issues with deadtime in the PET detector when
> validating my simulated PET system in GATE against my real PET system. My
> PET system is similar to a typical standard ring PET system. I have built a
> corresponding GATE model to it as close as I can. But the count rate in the
> GATE model is twice higher than the physical system. I think it is due to
> the weird behavior of deadtime in digitizer settings. Then I did some
> simple validation simulations to prove that. In my real system, 11.3 mci
> (equivalent to 19 kBq/ml) is high enough to paralyze the system, i.e., the
> collected coincidence rate would increase then decrease as decays go by.
> However, in the GTE model, I have not observed such a trend yet. Here is a
> simple example:
>
> [image: Screenshot from 2020-05-14 13-43-13.png]
> When I doubled the initial dose from 19 kBq/ml (11.3 mci) to 38 kBq/ml
> (22.6 mci), Gate also doubled the count of singles. To me, the deadtime
> module is not working. Because 19 kBq/ml is high enough to paralyze the
> detector, when the dose is doubled, it shall output ways less than twice of
> the singles.
>
> Another simulation I did to show GATE mode reacts to deadtime is varying
> the deadtime:
>
> [image: Screenshot from 2020-05-14 14-10-41.png]
> As you can see from the results above, the counts of singles barely change
> when deadtime increases from 10 ns to 100000 ns, which is very weird
> behavior to me. Also, 19 kBq/ml (11.3 mci) shall be high enough to paralyze
> the system.
>
> Please provide any clue or any help to correct it. Thank you very much.
> Sincerely,
> Zhengzhi
>
>
>
> Following is my digitizer settings:
> #=====================================================
> # D I G I T I Z E R: DETECTOR ELECTRONIC RESPONSE
> #=====================================================
> # A D D E R
> /gate/digitizer/Singles/insert adder
>
> # R E A D O U T
> /gate/digitizer/Singles/insert readout
> #/gate/digitizer/Singles/readout/setPolicy TakeEnergyCentroid
> #TakeEnergyWinner
> /gate/digitizer/Singles/readout/setDepth 5
>
> # E N E R G Y B L U R R I N G
> /gate/digitizer/Singles/insert blurring
> /gate/digitizer/Singles/blurring/setResolution 0.15
> /gate/digitizer/Singles/blurring/setEnergyOfReference 511. keV
>
> # E N E R G Y C U T
> /gate/digitizer/Singles/insert thresholder
> /gate/digitizer/Singles/thresholder/setThreshold 395. keV
> /gate/digitizer/Singles/insert upholder
> /gate/digitizer/Singles/upholder/setUphold 600. keV
>
> /gate/digitizer/Singles/insert timeResolution
> /gate/digitizer/Singles/timeResolution/setTimeResolution 0.700 ns
>
> # D E A D T I M E
> /gate/digitizer/Singles/insert deadtime
> /gate/digitizer/Singles/deadtime/setDeadTime 1000. ns
> /gate/digitizer/Singles/deadtime/setMode paralysable
> /gate/digitizer/Singles/deadtime/chooseDTVolume Crystal
>
>
> #=====================================================
> # C O I N C I D E N C E S O R T E R
> #=====================================================
> /gate/digitizer/Coincidences/setWindow 5. ns
> /gate/digitizer/Coincidences/minSectorDifference 1
> /gate/digitizer/Coincidences/setOffset 0. ns
> #/gate/digitizer/Coincidences/setMultiplePolicy killAll
> /gate/digitizer/Coincidences/describe
>
> /gate/digitizer/name delayedCoinc
> /gate/digitizer/insert coincidenceSorter
> /gate/digitizer/delayedCoinc/setOffset 90. ns
> /gate/digitizer/delayedCoinc/setWindow 5. ns
> /gate/digitizer/delayedCoinc/minSectorDifference 1
> /gate/digitizer/delayedCoinc/describe
>
> /gate/digitizer/name finalCoinc
> /gate/digitizer/insert coincidenceChain
> /gate/digitizer/finalCoinc/addInputName delayedCoinc
> /gate/digitizer/finalCoinc/addInputName Coincidences
> /gate/digitizer/finalCoinc/usePriority true
> /gate/digitizer/finalCoinc/insert deadtime
> /gate/digitizer/finalCoinc/deadtime/setDeadTime 10. ns
> /gate/digitizer/finalCoinc/deadtime/setMode paralysable
> /gate/digitizer/finalCoinc/describe
>
>
>
>
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