[Gate-users] Why the time difference has asymmetry shape?

[Simon Stute]

Hi,

If you plot only the non-random coincidences, I think you will have a
symmetric peak.

The asymmetric flat part of the profile probably comes from the random
coincidences.

With Monte Carlo simulations, the particles are tracked one by one. All
gammas contributing to an open coincidence window are buffered following
their track order.

So for two gammas coming from the same annihilation, the arrival time of
the first tracked particle can be after the second tracked particle and
vice-versa.

But for random coincidences, most of the time, the arrival time of the
first gamma will be before the arrival time of the second gamma, which
explains the asymmetric profile you get.

I think that you just have to randomize the order of the two gammas in each
coincidence to get a symmetric profile.

Regards,
Simon



On Tue, Aug 26, 2014 at 8:49 AM, 주요한 <yhjoo at gachon.ac.kr> wrote:

> Dear Gate users.
>
>
>
> I create a new PET system follows the Gate user manual. (my gate version
> is 6.2)
>
>
>
> Actually I try to do the simulation with point source, the result image
> shows a point also.
>
>
>
> And sinogram is also good.
>
>
>
> However, the time difference histogram is not common things.
>
>
>
> I attached it as image files in this e-mail.
>
>
>
> In real system, the random part of time histogram has a symmetry
> distribution.
>
>
>
> However it has asymmetry distribution in the simulation.
>
>
>
> Which part makes this?
>
>
>
> If you know or guess, please let me know. I want to fix it.
>
>
>
> Here is associated script..
>
>
>
> Thank you.
>
>
>
>
>
> /gate/digitizer/Singles/insert timeResolution
>
> /gate/digitizer/Singles/timeResolution/setTimeResolution 2.1 ns
>
>
>
> /gate/digitizer/Singles/insert deadtime
>
> /gate/digitizer/Singles/deadtime/setDeadTime 3000000. ps
>
> /gate/digitizer/Singles/deadtime/setMode nonparalysable
>
> /gate/digitizer/Singles/deadtime/chooseDTVolume level1
>
>
>
> /gate/digitizer/name Coincidences
>
> /gate/digitizer/insert coincidenceSorter
>
> /gate/digitizer/Coincidences/setInputName Singles
>
> /gate/digitizer/Coincidences/setWindow 20. ns
>
> /gate/digitizer/Coincidences/setOffset 0. ns
>
> /gate/digitizer/Coincidences/describe
>
>
>
> /gate/digitizer/name delay
>
> /gate/digitizer/insert coincidenceSorter
>
> /gate/digitizer/delay/setWindow 20. ns
>
> /gate/digitizer/delay/setOffset 500. ns
>
> /gate/digitizer/delay/describe
>
>
>
> /gate/digitizer/name finalCoinc
>
> /gate/digitizer/insert coincidenceChain
>
> /gate/digitizer/finalCoinc/addInputName delay
>
> /gate/digitizer/finalCoinc/addInputName Coincidences
>
> /gate/digitizer/finalCoinc/usePriority true
>
> /gate/digitizer/finalCoinc/describe
>
>
>
>
>
> Best Regards,
>
> Yohan
>
>
>
> _______________________________________________
> Gate-users mailing list
> Gate-users at lists.opengatecollaboration.org
> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
>
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