[Gate-users] about attenuation and sensitivity in GATE

[Susana Branco Silva]

Hi Hongwei,

 

If you want to “turn off” the attenuation information you don’t need to
define the phantom! You just need to define the source (shape; type of
source; distribution of the emission; placement of the source
).
And, if you want to “turn off” the physical effects (positron range,
scattering and photon accolinearity) you may use the gamma/gamma emission
source.

 

This choice (of these 2 turn off) allow to produce simulated data
representing an “acquisition best case scenario”.

 

 

Susana Branco Silva

 

untitled

Faculdade de Ciências da Universidade de Lisboa

Campo Grande, 1749-016 Lisboa, Portugal
Phone: (+351) 21 750 01 77 ext.: 20515
Fax:  (+351) 21 750 00 30

 <mailto:susana.silva at fc.ul.pt> email: susana.silva at fc.ul.pt

url: www.ibeb.fc.ul.pt

 

 

From: gate-users-bounces at lists.healthgrid.org
[mailto:gate-users-bounces at lists.healthgrid.org] On Behalf Of Hongwei Ye
Sent: sábado, 26 de Abril de 2008 0:14
To: gate-users at lists.healthgrid.org
Subject: [Gate-users] about attenuation and sensitivity in GATE

 


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/20080426/6483e39e/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 3122 bytes
Desc: not available
URL: <http://lists.opengatecollaboration.org/mailman/private/gate-users/attachments/20080426/6483e39e/attachment.gif>