[Gate-users] ERROR??? true coincidences from out of FOV

[Simon Stute]

Hi Hongwei,

Are you really sure that you attached every object of your scanner as
phantomSD (rsector, head, shielding, ...) ? and of course your cylinder too
?
I already encountered this problem before until I found that my rsectors
were not attach as phantomSD. So the scatter interactions came from here.

Good luck with that weird thing !
Simon

On Wed, Mar 4, 2009 at 4:57 PM, Hongwei Ye <howellye at yahoo.com> wrote:

> Dear GATE group and users,
>
> I found a wield thing when I simulated a LYSO-based PET system: the line
> source is put out of FOV and inside a polyethylene cylinder. The purpose of
> this simulation is to find how many scatters come from the source outside
> FOV.
>
> However, some true coincidences (about 1.5%) were found!! I have checked
> their annihiliation positions using ASCII output and they indeed came from
> the line source. If I connected two detecors using a line, annihilations
> CANNOT locate on this line ( not even close to). One example is given below.
> If you just checked Z positions and you can find the problem: 2.181e+02 for
> annihilation, 7.711e+01 for one single, and 1.479e+02 for another single.
> And NO scattering happens before photons entered the detectors.
>
> 0  608372     0 9.598e-01 -4.609e+01 2.181e+02
> 4.68951501753163224606169e+00 6.184e-01 -3.021e+02 -3.291e+02 7.711e+01
> 0    30     0     0   791     0      0     1     0     0 0.000e+00
> 0.000e+00
>
> 0  608372     0 9.598e-01 -4.609e+01 2.181e+02
> 4.68951501764343259281986e+00 4.892e-01 4.002e+02 1.912e+02 1.479e+02
> 0     3     0     0  1026     0      0     0     0     0 0.000e+00 0.000e+00
>
> Could anyone give explainations for this??  Thank you very much.
>
> Regards,
> Hongwei
>
>
>
>
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