Re: RE: [Gate-users] [ no subject ]

Wed Dec 19 10:19:00 CET 2007

Dear Min Jae and Yu Chen,

As you suggested, we performed the single_layer.mac simulation with 1/10 the source activity. Once again we obtained an energy spectra which does not fall to zero as expected (i.e. similar with the result using the higher source activity). The energy spectra is attached to this email as Gate312_single_layer_low_activ.ps. The output of the simulation for a low energy threshold of 400kev is:

There are: => 87053 singles
=> 3550 coincidences
=> 508 intercrystal coincidences
=> 110 randoms
=> 14 intercrystal randoms

We also ran the SAME simulation with 1/10 activity using Gate3.0.0 and got the expected energy spectra (Gate300_single_layer_low_activ.ps) and the following output:

There are: => 86057 singles 
           => 5246 coincidences
           =>  0 intercrystal coincidences
           =>  97 randoms
           =>  26 intercrystal randoms

We should point out that we have tested our simulations on two other computers in our department, in which GATE 3.1.2 has been installed by other colleagues. In each case, the PET benchmark was successfully completed but the results were not correct (i.e. the strange behaviour in the energy spectra). So, it really seems that the problem is not related to the computer used or with our installation of GATE.

Thanks for your help.
Jasmine and Irene

Original Message:

Dear MJ and others,
 
 I think what Irene et al reported is possible since
 benchmarkPET (and many other simulations) used blurring module
 (e.g., 26% resolution in benchmarkPET). This will simply smear 
 any small difference in no blurring application like Irene
 did.
 
 I am also puzzled by Irene's discovery:
 Single's energy goes above norminal input energy without blurring in GATE
 version 3.1.2.
 
 First, it is not likely a coincidence sorter problem (but that less coincidence
 events problem probably is.).
 
 I think the problem could be due to:
 
 1) GATE single (pulse) algorithm change?
 If an algorithm of single like all hits within a certain time window are collected and accounted
 for one pulse is implemented, it is possible to simulate pileup effect, and then we can see unreal larger energy for
 one single. 
 
 2) any change in Geant4?
 which corresponding Geant4 version?
 Is it possible that Genat4 loses correct track and time information for one event and wrongfully assigns those steps after
 a certain time to next event?
 
 To exclude those possibilities, a very low activity simulation will be helpful.
 
 Irene et al., can you do this: repeat your simualtion in v 3.1.2 at a very low activity? 
 
 Looking forward to seeing your new results.
 
 Yu Chen, Ph.D.
 University of Massachusetts Medical School
 Division of Nuclear Medicine
 55 Lake Avenue North
 Worcester, MA 01655-0243
 Phone: (508) 856-6123
 Fax: (508) 856-4572
 
 
 
 -----Original Message-----
 From: gate-users-bounces at lists.healthgrid.org on behalf of Park MinJae
 Sent: Mon 12/17/2007 8:20 PM
 To: 'Jasmine Schirmer'; gate-users at lists.healthgrid.org
 Subject: RE: [Gate-users] [ no subject ]
 
 Dear Irene,
 
 Let me check what you are saying...
 
 There is no problem with benchmarkPET...
 [In both the old and new versions of GATE, the benchmark PET was
 successfully completed and no difference in the energy spectra was
 observed.]
 
 In your simulation code, uphold value is 950 keV...
 [However, the upper energy threshold of the benchmark is set to
 650keV while our simulations are performed at higher upper energy
 thresholds.]
 [/gate/digitizer/Singles/upholder/setUphold 950. keV]
 
 In fact, I can't get that the benchmark is same but your code is
 different...
 
 Can I take a look on your code and simulate your code with my gate?
 
 MJ
 
 -----Original Message-----
 From: gate-users-bounces at lists.healthgrid.org
 [mailto:gate-users-bounces at lists.healthgrid.org] On Behalf Of Jasmine
 Schirmer
 Sent: Monday, December 17, 2007 11:24 PM
 To: gate-users at lists.healthgrid.org
 Subject: [Gate-users] [ no subject ]
 
 Dear GATE users and developers,
 
 A few weeks ago, we sent an email to the users list concerning a problem we
 are having with the newest version of GATE. The email was dated the 29th of
 November and is titled 'differences in energy spectra from different GATE
 releases'.
 
 At the moment, we can no longer use reliably the newest version of GATE
 until this issue is resolved. To recall your attention, we showed a
 difference in the energy spectra produced by two identical simulations using
 two versions of GATE (version 3.0.0 and the newest 3.1.2). The newest
 version gives a different and unexpected result for the energy spectra as
 you can see from the figures attached in the previous email. (The energy
 spectra does not fall to zero!)
 
 We kindly ask the developers and users to address this issue. In addition,
 if anyone would like to perform a similiar test on their version of GATE, we
 would be happy to provide the macro we used.
 
 Thanks in advance,
 Irene Torres and Jasmine Schirmer
 
 _______________________________________________
 Gate-users mailing list
 Gate-users at lists.healthgrid.org
 http://lists.healthgrid.org/mailman/listinfo/gate-users

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