<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
</head>
<body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">
<div><br>
</div>
Hi Patrick,
<div><br>
</div>
<div>how did you generate the plot with the two energy histograms?</div>
<div>Did you use a root-macro and could you send it to me/us to check,</div>
<div>whether I can reproduce it. It would save some time to possibly answer</div>
<div>your findings.</div>
<div><br>
</div>
<div>Thanks and kind regards,</div>
<div><br>
</div>
<div>Uwe Pietrzyk<br>
<div>
<div><span style="orphans: 2; widows: 2;">/----------------------------------------------------------------------</span></div>
<div style="orphans: 2; widows: 2;">Prof. Dr. Uwe Pietrzyk<br>
Diplom-Physiker<br>
Institut für Neurowissenschaften und Medizin / INM-4<br>
Forschungszentrum Jülich GmbH<br>
52425 Jülich<br>
Tel: +49-2461-61 4763<br>
Fax: +49-2461-61 2820<br>
Mobil: +49-162-103-4871<br>
eMail: <a href="mailto:U.Pietrzyk@fz-juelich.de">U.Pietrzyk@fz-juelich.de</a><br>
<a href="http://www.fz-juelich.de/inm/inm-4/DE/Home/home_node.html">http://www.fz-juelich.de/inm/inm-4/DE/Home/home_node.html</a><br>
&<br>
Bergische Universität Wuppertal<br>
Fachbereich C - Physik / D.08.01<br>
Gaußstr. 20<br>
42097 Wuppertal<br>
Tel: +49-(0)202-439-3523<br>
Fax: +49-(0)202-439-2811<br>
eMail: <a href="mailto:Uwe.Pietrzyk@physik.uni-wuppertal.de">Uwe.Pietrzyk@physik.uni-wuppertal.de</a><br>
<a href="http://www.medizinphysik.uni-wuppertal.de/">http://www.medizinphysik.uni-wuppertal.de</a><br>
----------------------------------------------------------------------/</div>
</div>
<br>
<div>
<div>On 04 Feb 2015, at 10:17, Patrick Hallen <<a href="mailto:patrick.hallen@rwth-aachen.de">patrick.hallen@rwth-aachen.de</a>> wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">Hi Paola,<br>
<br>
unfortunately it isn't caused by missing time blurring. I've had removed<br>
the time blurring from the attached example, to keep it as minimal as<br>
possible. It has always been included in our "real" PET simulation,<br>
which shows the same behavior.<br>
When I add time blurring to the attached minimal example, the two energy<br>
spectra stay the same.<br>
<br>
Best<br>
Patrick<br>
<br>
On 02/03/2015 05:23 PM, Paola Solevi wrote:<br>
<blockquote type="cite">Dear Patrick,<br>
could it be due to the time stamp?<br>
I see you don't apply any time blurring to your Singles so you preserve<br>
in your Singles list the ordering coming from the tracking of the photons.<br>
Try to apply the time blurring to your Singles to check if the effect<br>
smooths out.<br>
Hope it helps,<br>
p.<br>
<br>
<br>
<br>
On Tue, Feb 3, 2015 at 5:11 PM, Patrick Hallen<br>
<<a href="mailto:patrick.hallen@rwth-aachen.de">patrick.hallen@rwth-aachen.de</a> <<a href="mailto:patrick.hallen@rwth-aachen.de">mailto:patrick.hallen@rwth-aachen.de</a>>><br>
wrote:<br>
<br>
Hello,<br>
<br>
I've discovered a weird inconsistency in the energy spectra of the two<br>
photons of the coincidences. Attached you can find the histograms of<br>
Coincidences/energy1 and Coincidences/energy2, i.e. the energy spectra<br>
of the two 511 keV photons of a coincidence. I would expect, that the<br>
two spectra would look the same (except for statistic fluctuations), but<br>
you can clearly see, that the spectrum of the second photon has distinct<br>
statistically significant peaks in the compton region, which are lacking<br>
in the spectrum of the first photon.<br>
<br>
I've observed this feature first with the simulation of our cylindrical<br>
PET scanner, which lead me to create a minimal example to reproduce this<br>
(see attached minimal.mac). The minimal example consists of just two<br>
opposing blocks of LYSO scintillator and a mono-energetic 511 keV<br>
back-to-back photon source. The attached spectrum is the result of this<br>
simulation, but the spectra for our more complex cylindrical PET<br>
simulation looks similar.<br>
<br>
I've tried changing different things in the simulation, like the<br>
radiation source (F18, C11) or the detector material (Water), with the<br>
same result: The spectra of the two photons are significantly different<br>
from each other. I could also reproduce this with the provided example<br>
PET_CylindricalPET_System.mac, after I reduced the energy threshold to<br>
include the compton region.<br>
<br>
I am observing this with GATE 7.0 and GEANT4 9.6.3, both compiled from<br>
source and using vGATE 3.0.<br>
<br>
There seems to be some weird bias in the selection which of the two<br>
photons is the first and which the second photon. By looking at the GATE<br>
code, I couldn't find any obvious source of this. Usually one would<br>
expect that the energy deposition of the two photons are totally<br>
uncorrelated, which would result in the same energy spectra (except for<br>
statistical fluctuations).<br>
<br>
I suspect a bug, which might influence important PET performance<br>
parameters such as the sensitivity, which depends on the energy<br>
threshold. For a preclinical PET scanner one usually choses a small<br>
energy threshold to increase the sensitivity, since the compton scatter<br>
most often takes place in the detector and not in the object. When the<br>
energy in the compton region would be wrong, this could potentially<br>
result in a wrong simulated sensitivity.<br>
<br>
Kind regards,<br>
Patrick Hallen<br>
<br>
_______________________________________________<br>
Gate-users mailing list<br>
<a href="mailto:Gate-users@lists.opengatecollaboration.org">Gate-users@lists.opengatecollaboration.org</a><br>
<<a href="mailto:Gate-users@lists.opengatecollaboration.org">mailto:Gate-users@lists.opengatecollaboration.org</a>><br>
<a href="http://lists.opengatecollaboration.org/mailman/listinfo/gate-users">http://lists.opengatecollaboration.org/mailman/listinfo/gate-users</a><br>
<br>
<br>
</blockquote>
_______________________________________________<br>
Gate-users mailing list<br>
<a href="mailto:Gate-users@lists.opengatecollaboration.org">Gate-users@lists.opengatecollaboration.org</a><br>
http://lists.opengatecollaboration.org/mailman/listinfo/gate-users<br>
</blockquote>
</div>
<br>
</div>
<br>
<font face="Arial" color="Black" size="1"><br>
------------------------------------------------------------------------------------------------<br>
------------------------------------------------------------------------------------------------<br>
Forschungszentrum Juelich GmbH<br>
52425 Juelich<br>
Sitz der Gesellschaft: Juelich<br>
Eingetragen im Handelsregister des Amtsgerichts Dueren Nr. HR B 3498<br>
Vorsitzender des Aufsichtsrats: MinDir Dr. Karl Eugen Huthmacher<br>
Geschaeftsfuehrung: Prof. Dr.-Ing. Wolfgang Marquardt (Vorsitzender),<br>
Karsten Beneke (stellv. Vorsitzender), Prof. Dr.-Ing. Harald Bolt,<br>
Prof. Dr. Sebastian M. Schmidt<br>
------------------------------------------------------------------------------------------------<br>
------------------------------------------------------------------------------------------------<br>
<br>
</font>
</body>
</html>