[Gate-users] Energy spectrum in simple CZT SPECT setup (Simon Stute)

Chen, Yu Yu.Chen at umassmed.edu
Fri Oct 1 21:03:15 CEST 2010


Hi, Phillipp,

The hit in GATE (also Geant4) actually represents one step in particle tracking. The step length is dependent on a parameter setting called Interaction Length. The number of steps in a particular volume (such as one crystal) for a particular particle (photons, electrons, protons, etc.) of course may be different. 

By the way, in old Geant4 versions, there is no standard Rayleigh process. I haven't checked it for the recent versions (I assume it is still not).
Remember that the standard model is a paramerization of data and valid for Energy > 10 keV
while the low energy model is an instant fitting of experimental data (which are read in at the very beginning of the simulation and more time-consuming).

Hope this helpful.

Yu 


Message: 1
Date: Thu, 30 Sep 2010 15:23:07 +0200
From: Philipp Matthies <philipp.matthies at googlemail.com>
Subject: Re: [Gate-users] Energy spectrum in simple CZT SPECT setup
        (Simon  Stute)
To: gate-users at lists.opengatecollaboration.org
Message-ID: <FB86980C-4AFC-4708-9396-3D65525267B3 at gmail.com>
Content-Type: text/plain; charset=us-ascii

Hi Simon,

ah, that's a very good point and totally makes sense!
I didn't set any digitizer modules, so I have set an adder module now and ran the simulation again and I could see a perfectly sharp photo peak.
And as you can see in the G4history.macro (didn't you receive the attachments?) I set the physics to be like that:

/gate/physics/gamma/selectRayleigh lowenergy
/gate/physics/gamma/selectPhotoelectric lowenergy
/gate/physics/gamma/selectCompton lowenergy
/gate/physics/gamma/selectGammaConversion lowenery

I thought (obviously wrong) that the photoelectric effect would be one interaction, e.g. one hit.

Thanks a lot,

Philipp Matthies




Am 30.09.2010 um 12:00 schrieb gate-users-request at lists.opengatecollaboration.org:

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>  1. Re: Energy spectrum in simple CZT SPECT setup (Simon Stute)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 30 Sep 2010 11:04:02 +0200
> From: Simon Stute <gate.stute at gmail.com>
> Subject: Re: [Gate-users] Energy spectrum in simple CZT SPECT setup
> To: Philipp Matthies <philipp.matthies at googlemail.com>
> Cc: gate-users at lists.opengatecollaboration.org
> Message-ID:
>       <AANLkTikakHLDdgM7oJmbjxMDMCdRn=d2xX8iOe1c2GpJ at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi Philipp,
>
> You say you are looking at singles, but singles are formed from hits, and
> hits (real interactions) are combined by an adder module to give singles.
> So did you use at least an adder in the digitizer ?
> Did you assigned a physics package to the compton and photoeletric effects ?
> I don't know what is the default if you don't give the following commands
> explicitly :
>
> gate/physics/gamma/selectPhotoelectric    [lowenergy, standard, inactive]
> gate/physics/gamma/selectCompton    [lowenergy, standard, inactive]
> gate/physics/gamma/selectRayleigh    [lowenergy, standard, inactive]
>
> 5mm depth for your "crystal" is also sufficient, but try to put much more.
>
> Hope this helps,
> Simon
>
>
> On Thu, Sep 30, 2010 at 10:31 AM, Philipp Matthies <
> philipp.matthies at googlemail.com> wrote:
>
>> Hello,
>>
>> I set up a very basic simulation with only a CZT crystal and a point
>> source, nothing more. I'm using GATE v5 under Mac OS X.
>>
>> In the screenshot I plotted a few variables from the Singles tree of the
>> ROOT output. Can anybody explain the energy spectrum to me?
>> I didn't set any digitizer options and the source is monoenergetic
>> (140.5keV) so I expected so see a clear photopeak at 140.5keV and the
>> characteristic compton spectrum.
>> Instead there appear like two peaks between around 105keV and 115keV and a
>> few more at lower energies. No photopeak, no compton spectrum, nothing like
>> I expected it to be.
>>
>> The setup was as followed:
>> - world volume 20 x 20 x 20 cm^3 air
>> - CZT crystal (4.0 x 4.0 x 0.5cm^3) set as sensitive detector
>> - point source of 140.5keV and 1MBq at a distance of 5cm centered in front
>> of the crystal
>> - no digitizer
>>
>> For the whole script with all variables set see attached file
>> G4History.macro.
>>
>>
>> Kind regards,
>>
>> Philipp Matthies
>>
>> ---------------------------------------------------------
>> Physics Department, TU Munich
>> Nuclear medicine, Klinikum rechts der Isar, Munich
>> SurgicEye GmbH, Munich
>>
>>
>>
>>
>> _______________________________________________
>> Gate-users mailing list
>> Gate-users at lists.opengatecollaboration.org
>> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
>>
>
>
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------------------------------

Message: 2
Date: Fri, 1 Oct 2010 11:36:01 +0200
From: Simon Stute <gate.stute at gmail.com>
Subject: Re: [Gate-users] Energy spectrum in simple CZT SPECT setup
        (Simon  Stute)
To: Philipp Matthies <philipp.matthies at googlemail.com>
Cc: gate-users at lists.opengatecollaboration.org
Message-ID:
        <AANLkTi=n+9SyAgnjJdRtQffQ7WSiEuJ9jCo-i304Rh5r at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Hi Philipp,

On Thu, Sep 30, 2010 at 3:23 PM, Philipp Matthies <
philipp.matthies at googlemail.com> wrote:

> Hi Simon,
>
> ah, that's a very good point and totally makes sense!
> I didn't set any digitizer modules, so I have set an adder module now and
> ran the simulation again and I could see a perfectly sharp photo peak.
>


OK good !



> And as you can see in the G4history.macro (didn't you receive the
> attachments?) I set the physics to be like that:
>
> /gate/physics/gamma/selectRayleigh lowenergy
> /gate/physics/gamma/selectPhotoelectric lowenergy
> /gate/physics/gamma/selectCompton lowenergy
> /gate/physics/gamma/selectGammaConversion lowenery
>


OK I just looked at the screenshot, and it is OK.



>
> I thought (obviously wrong) that the photoelectric effect would be one
> interaction, e.g. one hit.
>


I am clearly not an expert in particle physics ! so I let someone else
(maybe ?) explain you what really happens :-)

Cheers,
Simon



>
> Thanks a lot,
>
> Philipp Matthies
>
>
>
>
> Am 30.09.2010 um 12:00 schrieb
> gate-users-request at lists.opengatecollaboration.org:
>
> > Send Gate-users mailing list submissions to
> >       gate-users at lists.opengatecollaboration.org
> >
> > To subscribe or unsubscribe via the World Wide Web, visit
> >       http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
> > or, via email, send a message with subject or body 'help' to
> >       gate-users-request at lists.opengatecollaboration.org
> >
> > You can reach the person managing the list at
> >       gate-users-owner at lists.opengatecollaboration.org
> >
> > When replying, please edit your Subject line so it is more specific
> > than "Re: Contents of Gate-users digest..."
> >
> >
> > Today's Topics:
> >
> >  1. Re: Energy spectrum in simple CZT SPECT setup (Simon Stute)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Thu, 30 Sep 2010 11:04:02 +0200
> > From: Simon Stute <gate.stute at gmail.com>
> > Subject: Re: [Gate-users] Energy spectrum in simple CZT SPECT setup
> > To: Philipp Matthies <philipp.matthies at googlemail.com>
> > Cc: gate-users at lists.opengatecollaboration.org
> > Message-ID:
> >       <AANLkTikakHLDdgM7oJmbjxMDMCdRn=d2xX8iOe1c2GpJ at mail.gmail.com>
> > Content-Type: text/plain; charset=ISO-8859-1
> >
> > Hi Philipp,
> >
> > You say you are looking at singles, but singles are formed from hits, and
> > hits (real interactions) are combined by an adder module to give singles.
> > So did you use at least an adder in the digitizer ?
> > Did you assigned a physics package to the compton and photoeletric
> effects ?
> > I don't know what is the default if you don't give the following commands
> > explicitly :
> >
> > gate/physics/gamma/selectPhotoelectric    [lowenergy, standard, inactive]
> > gate/physics/gamma/selectCompton    [lowenergy, standard, inactive]
> > gate/physics/gamma/selectRayleigh    [lowenergy, standard, inactive]
> >
> > 5mm depth for your "crystal" is also sufficient, but try to put much
> more.
> >
> > Hope this helps,
> > Simon
> >
> >
> > On Thu, Sep 30, 2010 at 10:31 AM, Philipp Matthies <
> > philipp.matthies at googlemail.com> wrote:
> >
> >> Hello,
> >>
> >> I set up a very basic simulation with only a CZT crystal and a point
> >> source, nothing more. I'm using GATE v5 under Mac OS X.
> >>
> >> In the screenshot I plotted a few variables from the Singles tree of the
> >> ROOT output. Can anybody explain the energy spectrum to me?
> >> I didn't set any digitizer options and the source is monoenergetic
> >> (140.5keV) so I expected so see a clear photopeak at 140.5keV and the
> >> characteristic compton spectrum.
> >> Instead there appear like two peaks between around 105keV and 115keV and
> a
> >> few more at lower energies. No photopeak, no compton spectrum, nothing
> like
> >> I expected it to be.
> >>
> >> The setup was as followed:
> >> - world volume 20 x 20 x 20 cm^3 air
> >> - CZT crystal (4.0 x 4.0 x 0.5cm^3) set as sensitive detector
> >> - point source of 140.5keV and 1MBq at a distance of 5cm centered in
> front
> >> of the crystal
> >> - no digitizer
> >>
> >> For the whole script with all variables set see attached file
> >> G4History.macro.
> >>
> >>
> >> Kind regards,
> >>
> >> Philipp Matthies
> >>
> >> ---------------------------------------------------------
> >> Physics Department, TU Munich
> >> Nuclear medicine, Klinikum rechts der Isar, Munich
> >> SurgicEye GmbH, Munich
> >>
> >>
> >>
> >>
> >> _______________________________________________
> >> Gate-users mailing list
> >> Gate-users at lists.opengatecollaboration.org
> >> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
> >>
> >
> >
> > ------------------------------
> >
> > _______________________________________________
> > Gate-users mailing list
> > Gate-users at lists.opengatecollaboration.org
> > http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
> >
> > End of Gate-users Digest, Vol 52, Issue 25
> > ******************************************
>
> _______________________________________________
> Gate-users mailing list
> Gate-users at lists.opengatecollaboration.org
> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users
>


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