[Gate-users] Problem with the coincidence

Tue Apr 20 15:19:13 CEST 2010

Hi Simon,

The attachment is the ditribution of the time difference of singles in
coincidence. The result has two groups. One is from the simulation in which
there is a point source centered in FOV and no phantom used. Another is from
the simulation in which there is a cylinder source and a cylinder phantom
centered in FOV. The time resolution is set to 0 and three coincidence
window are used. For three different coincidence window, the resulted data
are obtained from same simulated hits data with DigiGATE.

When I get the distribution,  I compute the absolute value of time
difference of two singles in each coincidence. So in the figures, the point
in timebin 0~500 is the distribution I got while point in timebin -500~0 is
a copy of timebin 0~500. The reason to do this is only for getting a fitting
curve. Maybe you can get something from these figures! Now, I plan to
program by myself to do the coincidence with simulated singles.

Thanks,
Jinxia

在 2010年4月20日 下午7:06，Simon Stute <gate.stute at gmail.com>写道：

> 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
>>
>
>

-- 
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
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