[Gate-users] about attenuation and sensitivity in GATE

[Hongwei Ye]

Dear All,

I'm wondering if there is any way to turn off the attenuation in GATE 
(because I'd like to use a simulation without attenuation in 
reconstruction). 

What I did right now is to use "Air" to replace "Water" (or something 
else) for the object material. But I met a problem here:

I have tested two simulations: same objects with same activity, same scan 
time, but simulation 1 is made by "Air" and simulation 2 is made by 
"Water". Guess what I got? Simulation 2 (13920 counts) had more 
coincidences than simulation 1 (8646 counts) even if simulation 2 was 
supposed to be attenuated more by water. (I attached .mac file here)

Can anyone explain this phenomena or guide me how to turn off the 
attenuation ? Should I use "Vacuum" instead of "Air" and set up "back to 
back gamma source"? 

One more question is about the sensitivity: what is its range for ECAT 962 
system? By roughly calculating, I got 20~50 cps/kBq depending on different 
objects. It seems to me those number are too high.

Thanks a lot.

Regards,
Hongwei



_____________________________________________________________________________
Scanned by IBM Email Security Management Services powered by MessageLabs. For more information please visit http://www.ers.ibm.com
_____________________________________________________________________________
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.opengatecollaboration.org/mailman/private/gate-users/attachments/20080425/48a02162/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: cross_042508.mac
Type: application/octet-stream
Size: 16907 bytes
Desc: not available
URL: <http://lists.opengatecollaboration.org/mailman/private/gate-users/attachments/20080425/48a02162/attachment.obj>