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

[Philipp Matthies]

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:

> 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
> ******************************************