[Gate-users] Preprocessing Hits file or adding layerIDs

[David Oxley]

Dear Gate-Users, 

I am not greatly experienced with GATE and am struggling to get it to do quite what I want, perhaps someone can help. 
I am using GATE v6.0.0 on Ubuntu 10.04 and am simulating a full-ring, cylindrical PET scanner. 
I do not have a fixed scanner design, so am working with a generic, continuous cylindrical volume and will digitize/voxelise the data offline.

My problem is that I want to keep track of all Compton and Photoelectric events, but, if possible, want to avoid processing the Hits file as I am not interested in the 10-20 collisions of the electron. For each of the ~15 lines it generates I am only interested in 2.  In a sense, I want the photon hits only. 
I have tried changing my electron cut value to very large values, but still see electrons in the Hits file.

>From what I can gather even the SinglesAdder file will still add a Compton and a photoelectric effect if they are in the same volume. I want to avoid this, and see the following options. 
1)
Define volumes as small as the finest resolution I am interested in (~order of mm-s). Of course this is inefficient, but more problematic is that I run out of layerIDs to play with. It seems there are only 5. But if I make a continuous ring (which I do want to make) I would need at least 50 different layers of 1mm each. 

2)
Apply some sort of cut to the hits file, to sum the electron deposits into the Compton deposits (as these are zero). 

Has anyone else had similair difficulties? Is it possible (advisable?) to add layerIDs to the source code, if so could someone point me in the right direction? 
Is there a way to filter the Hits file, without summing inside volumes? 

I appreciate that it is perhaps unorthodox to want to keep two interactions, even if there were only in one crystal, but I hope it is still possible. 

I hope my message is clear, but please get back to me if there are questions. Thanks in advance for any help. 

Kind regards,

Dave Oxley 

================================= 

Dr. David Oxley

Postdoctoral Researcher 
Kernfysisch Versneller Instituut
Zernikelaan 25
NL-9747 AA Groningen
The Netherlands

d.c.oxley at kvi.nl
d.c.oxley at rug.nl