[Gate-users] Problem with the coincidence

[Simon Stute]

Hi Jinxia,

2010/4/20 Jinxia Guo <jinxia.guo2009 at gmail.com>

> Hi Simon,
>
> Thanks for your answer. I have do some other simulation too. In all
> simulation, the time resolution is set to 0 and I get the distribution of
> time difference of all counts. I can't find the anything to help me
> understand that the time difference of singles in a coincidences is larger
> than coincidence window. According to the fig.8.5 in GATE user guide, it can
> be considered as a coincidence only if the singles are in the coincidence
> time window. So the time difference of singles in a coincidence shouldn't be
> larger than the coincidence window. I can't understand that you said “ if
> you have a sort a gaussian function, or a dirac function at a certain time
> difference value”. Can you explain for me?
>
>

I agree with you that there is something strange in the fact that some
coincidences have a delta time greater than the given time window. But I
would like to know and even see on a plot the distribution of time
differences of all counts, to see if that distribution stops as a dirac
function at a certain value or if it decreases slowly after the expected
value. This could give a hint trying to understand where does the problem
come from.



> For the " multiple coincidences" problem, there are 9 policies to choose
> and I choose the default policy in the simulation. I can understand the
> result now. But I have another question. The policy "take Winner Of Goods"
> means "Only the good sub-pair with the highest energy is taken". Why choose
> the highest energy subpair? To avoid scatters?
>
>

Yes probably. But 9 policies are proposed in order to find the one most
appropriated to the system you simulate.

Cheers,
Simon



> Thanks,
> Jinxia
>
>
> 在 2010年4月19日 下午5:09，Simon Stute <gate.stute at gmail.com>写道：
>
> Hi,
>>
>> 2010/4/19 Jinxia Guo <jinxia.guo2009 at gmail.com>
>>
>> Dear gate users,
>>>
>>> I encountered a problem when I inspection the time difference of two
>>> singles
>>> in a coincidence. In the simulation, there are many coincidences in which
>>> the time difference of two singles is larger than the coincidence window.
>>> I
>>> do two simulation. In the first one, the time resolution is set to 200ps
>>> and
>>> the coincidence window is set to 200ps. In the second one, the time
>>> resolution is set to 0 and the coincidence window is set to 200ps. In
>>> both
>>> simulation, the problem exists. I can't find why this happened with
>>> chapter8
>>> of GATE user guide. So who know how gate does its coincidence？Why the
>>> time
>>> difference of singles in coincidences is larger than the coincidence
>>> window?
>>>
>>>
>>
>> You can plot the time difference, in order to have an idea of what the
>> problem really looks like, it would be a good start.
>> For example to see if you have a sort a gaussian function, or a dirac
>> function at a certain time difference value, it would be easier to try to
>> understand the problem.
>> And to study the problem, just set the time resolution to 0, otherwise it
>> would be too difficult to analyse the results.
>>
>>
>>
>>> In addition to the above simulation, I do another two simulation. In
>>> first
>>> one, the time resolution is 300ps and coincidence window is 10ns. In
>>> second
>>> one, the time resolution is 300ps too and coincidence window is 100ns. I
>>> found there are more coincidences in the first simulation than in the
>>> second
>>> simulation,about five times larger.Then who can explain it？
>>>
>>>
>>
>> By setting your time window to 100ns, you will have a lot of multiple
>> coincidences, so it depends on what policy you choose.
>> By default, takeTheWinner is chosen, so it explains why you get five times
>> less coincidences in your second simulation.
>> See the user's guide.
>>
>> Cheers,
>> Simon
>>
>>
>>> By the way, in all simulations, the diameter of simulated PET ring is
>>> about
>>> 82cm. And the simulation time is the same.
>>>
>>> Hope for help. Thank you!
>>>
>>> -
>>> Jinxia Guo
>>> School of Life Sci&Tech
>>> D11 Building Room 503
>>>
>>> Huazhong Univ. of Sci. & Tech
>>>
>>> 1037 Luoyu Road, Wuhan 430074, China
>>> Tel:+86-27-8779-2294
>>> _______________________________________________
>>> Gate-users mailing list
>>> Gate-users at lists.opengatecollaboration.org
>>> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
>>
>>
>>
>
>
> --
> Jinxia Guo
> School of Life Sci&Tech
> D11 Building Room 503
>
> Huazhong Univ. of Sci. & Tech
>
> 1037 Luoyu Road, Wuhan 430074, China
> Tel:+86-27-8779-2294
>