[Gate-users] Photon ID issue in F18 simulation

[sd48 at buffalo.edu]

Hi All,
          I'am facing the following issue with regards to the simulation of 
a Flour-18 "positron" isotope :

* After running the simulation and generating the "root" file, the root 
file is subjected to "Coincidence Classification" to obtain the counts for 
the different coincidences. The resulting values            show a very 
high value for the "Non-annihilation" Coincidence (NAC)count, which one 
expects to be almost zero for F18.

* On analyzing the source code(in the Gate package) for the generation of 
"photonID" values which are sampled by us (to obtain "photonID1" and 
"photonID2" used in co-incidence classification),we see  that "photonID" 
takes on the value of "zero" numerous times. More specifically,in the 
"GateTrajectoryNavigator.cc" source file the condition "if(photonID == 
rootID)" where rootID=0 is satisfied quite a few times in every set of 
"Hits" being processed.The reason one is concerned about the value zero is, 
in our classification if one of the two photonID values (either photonID1 
or photonID2) is set to zero, then that particular coincidence is 
classified as NAC.

             Hence, i would like to know if this condition while simulating 
a F18 isotope is indeed acceptable. If so, then what is the significance of 
the photonID being given the value of zero. Can some please provide some 
pointers in this regard. Thanks.

regards,
Srinivas

---------------------
Srinivas Prasad D.G.
Research Assistant,
Department of Nuclear Medicine.
University at Buffalo, State University of New York,
Buffalo, NY.