[Gate-users] CylindricalPET inside a large lead box or cylinder ?

[Simon Stute]

Hi Sanae,

2008/1/25, Sanae Rechka <Sanae.Rechka at usherbrooke.ca>:
>
>
> Hi Simon,
>
> Done :  I confirmed by simulation what was said in the Gate users Guide :
> we can
> only record Hits in volumes belonging to the scanner.
>
> I tried the two solutions you proposed, but they don't work. And as you
> said
> there is no solution without modifying the gate source code.


OK, too bad ...
Nevertheless, perhaps I have a solution, but it is a do-it-yourself method !

If you build a very very large cylindricalPET (I mean your original scanner
but where rsectors have a huge length on z axis, ideally infinity !) you
could stop almost every gammas which should go outside your original
scanner. Then everything will be done in the postprocessing. Assuming the z
length of your rsector from your original scanner is zOrig, and the output
format is ROOT. Then for each Singles, you take the globalPosZ variable
(which represents the z cartesian coordinate where your gammas was detected)
and you check whether this variable is lower than -zOrig/2 or higher than
+zOrig/2. If it's the case then it means that your gamma should go outside
your original scanner and so you can get the energy and everything that you
are looking for. The only problem is how big your z length should be to get
the lower error and to loose the lower quantity of  the emitted gammas.

I realise now that maybe you want to get photons that go inside your
crystals and then go outside without doing a photoelectric interaction. In
this case, you have to build deeper rsectors and crystals than the original
ones and proceed with the same idea. You take the globalPosX and globalPosY
variables, then calculate the angle of the position from the x axis (or y
axis), then calculate with that angle the maximum xOrig and yOrig values
from where your photon will be outside the original rsector and see by doing
an other calculation if your x and y values are higher (or lower, it depends
on the angle value) than the xOrig and yOrig values, which means that the
photon is out of your original scanner !!! Very simple ;-) It's really much
more complicated than the first method but it depends on what you want to
get.

Am I clear in this message, do I really understand what you want to do ?
In any case, I hope this will work,

Cheers,
Simon

Thanks and Have a nice day
> Sanae
>
>
>
>
>
>
> ----- Message transféré de Sanae Rechka <Sanae.Rechka at USherbrooke.ca>
> -----
>    Date : Thu, 24 Jan 2008 18:54:00 -0500
>      De : Sanae Rechka <Sanae.Rechka at USherbrooke.ca>
> Adresse de retour :Sanae Rechka <Sanae.Rechka at USherbrooke.ca>
>   Sujet : Re: [Gate-users] CylindricalPET inside a large lead box or
> cylinder ?
>       À : Simon Stute <gate.stute at gmail.com>
>
> Hi Simon,
>
> Thank you very much for your answer,
>
> - But if we define the world material to lead, can we record Hits in the
> world
> material ?  even If Gate only stores hits for those volumes attached to a
> sensitive detector and belonging to a system.  And system should be one of
> the
> systems defined in page 48 of the Gate users Guide (which mean
> CylindricalPET,
> SPECT, ECAT, etc...) ?????
>
> - for the second solution : to define a big lead box over your
> CylindricalPET,
> in lead your gammas will be stopped before traversing one mm ! so they
> won't
> escape from your box and you will not be able to see them after.
>
> This is Ok, it's what I need. But can we record Hits in the Box over the
> scanner
> ? because according to the GATE users Guide we can only record Hits in
> volumes
> belonging to the scanner ? isn't it ?
>
>
>
> Sanae
>
>
>
>
>
>
>
>
>
>
> Selon Simon Stute <gate.stute at gmail.com>:
>
> > Hi,
> >
> > 2008/1/24, Sanae Rechka <Sanae.Rechka at usherbrooke.ca>:
> > >
> > >
> > > Dear Gate users,
> > >
> > > Is it possible to place the CylindricalPET inside a large lead box or
> > > cylinder
> > > to store the energy of photons outside the scanner (photons which
> escape
> > > from
> > > the scanner)?
> >
> >
> > One possibility is to define the world material to lead, an other is to
> > define a big lead box over your CylindricalPET, but there is no interest
> to
> > do such a thing because in lead your gammas will be stop before
> traversing
> > one mm ! so they won't escape from your box and you will not be able to
> see
> > them after. I don't really see a solution to your investigation at the
> > moment but if I have an idea, I will send you (but I think this is not
> > possible without modifying the gate source code and even the geant4
> source
> > code !)
> >
> > Good luck !
> > Simon
> >
> > Of course, I am aware of this :
> > >                           Gate only stores hits for those volumes
> attached
> > > to a
> > > sensitive detector. A volume must belong to a system before it can be
> > > attached
> > > to a sensitive detector.  And system should be one of the systems
> defined
> > > in
> > > page 48 of the Gate users Guide. I'm aware of that.  And it's why I'm
> > > asking....
> > >
> > >
> > > Can any body answer my question please ?
> > >
> > > Thank you very much in beforehand
> > >
> > >
> > > Sanae
> > >
> > >
> > > _______________________________________________
> > > Gate-users mailing list
> > > Gate-users at lists.healthgrid.org
> > > http://lists.healthgrid.org/mailman/listinfo/gate-users
> > >
> >
>
>
>
>
>
> ----- Fin du message transféré -----
>
>
>
>
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