[Gate-users] Photons on a ring surface, new detector implementation and readout and new time management

[Chen, Yu]

Hi, Miguel, 

Nice questions. 
I would provide you my opinion on your first question.


First, let me ask you a question. What is the material you used in your
0.1mm thick crystal? If it is a *NORMAL* (e.g., GSO) crystal, of course
we should expect a little edep in this thin layer.

Instead, you can describe a virtual material with very large density,, letting
photons be stopped completely within one step in this thin layer. Then you can figure out
what are those photon's position, momentum from hit file.  

Another way is to modify GateSteppingFunction (correct name?) and let a track be killed
when it reaches crystalSD.

My two cents. Hope it helps.


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 Miguel Couceiro
Sent: Sun 4/29/2007 7:41 PM
To: Gate-users at lists.healthgrid.org
Subject: [Gate-users] Photons on a ring surface, new detector implementation and readout and new time management
 
Hi all!


Is there any way to use GATE to simulate the interaction of photons 
within phantoms and propagate them to the surface of an annulus, and 
then save the information needed to continue the simulation in Geant4?
This is easy to do in Geant4, but I would like to use voxelized phantoms.

I have tried to define a cylindricalPET whith 0.1 mm thick, and disable 
the module, submodule, etc., and attach the crystalSD to the 
cylindricalPET. However, the edep of the Hits file is very low, as 
expected, and there is no information on photon momentum to proceed the 
simulation in Geant4.

Do you think that creating another sensitive detector, for instance the 
cylindricalSD, and getting the pre-step point information would solve 
the problem?



Another possibility is to implement in GATE the detector that I want to 
simulate (not crystal based). This means to implement, at least, a new 
system and readout. Were can I find enough information to do this?



My last question concerns the Time Management. Sometimes we perform a 
complete simulation with only one isotope, with the correct digitizer 
sequence. Then we want to change the activity, for instance to study the 
count rate performance. Since digigate is must faster then a complete 
simulation, we could benefit if instead of a single time stamp for 
singles there was three time stamps: one for positron annihilation, one 
for photon interaction in the detector after annihilation, and one that 
would be the sum of the two. This first one could be changed by the 
digitizer based on the source activity, and last one could be calculated 
based on the first and second ones. Is there any way to use this 
approach in digigate?


Thanks in advance for your answers,
Miguel
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