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

[Simon Stute]

Hi,

To remove random coincidences, you mean that you specify in your analysis
that you take only coincidences where eventID1 equals eventID2 ?
The profile cannot have only one side, because the first tracked particle
will not obviously be the first one to be detected, and furthermore the use
of the time resolution module can even change the order of arrival of the
two photons.

Regards,
Simon



> On Wed, Aug 27, 2014 at 8:53 AM, Yohan <yhjoo at gachon.ac.kr> wrote:
>
>> Dear Simon
>>
>>
>>
>> Thank you for your response.
>>
>>
>>
>> Actually the result is extracted from coincidence data. (which is not
>> include the random coincidences)
>>
>>
>>
>> As your recommendation, if I randomize the order of the two gammas in
>> each coincidence, then I can get a symmetric profile.
>>
>>
>>
>> However I just want to confirm whether my data is correct or not.
>>
>>
>>
>> As your description about random coincidence, I guess the asymmetric
>> profile may come form that if the Gate simulation record first event with
>> the first event.
>>
>>
>>
>> In this case, the profile has to have one side. It shouldn’t have a value
>> more than 0.
>>
>>
>>
>> However the result doesn’t show that.
>>
>>
>>
>> I appreciate you that you recommend the method to make a symmetry
>> profile.
>>
>>
>>
>> But I just wonder still.
>>
>>
>>
>> Why..?
>>
>>
>>
>> Is there any problem with my GATE simulation?
>>
>>
>>
>> Maybe this will be my homework. J
>>
>>
>>
>> Thank you.
>>
>>
>>
>>
>>
>>
>>
>> Best Regards,
>>
>> Yohan
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> *From:* Simon Stute [mailto:gate.stute at gmail.com]
>> *Sent:* Tuesday, August 26, 2014 6:06 PM
>> *To:* 주요한
>> *Cc:* gate-users at lists.opengatecollaboration.org
>> *Subject:* Re: [Gate-users] Why the time difference has asymmetry shape?
>>
>>
>>
>> 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
>>
>>
>>
>>
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>>
>>
>>
>
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