<html><head><style type="text/css"></style></head><body><div style="font-family:times new roman,new york,times,serif;font-size:12pt">Dear GATE group and users,<br><br>I found a wield thing when I simulated a LYSO-based PET system: the line source is put out of FOV and inside a polyethylene cylinder. The purpose of this simulation is to find how many scatters come from the source outside FOV.<br><br>However, some true coincidences (about 1.5%) were found!! I have checked their annihiliation positions using ASCII output and they indeed came from the line source. If I connected two detecors using a line, annihilations CANNOT locate on this line ( not even close to). One example is given below. If you just checked Z positions and you can find the problem: 2.181e+02 for annihilation, 7.711e+01 for one single, and 1.479e+02 for another single. And NO scattering happens before photons entered the detectors.<br><br>0  608372     0 9.598e-01 -4.609e+01 2.181e+02 4.68951501753163224606169e+00 6.184e-01 -3.021e+02 -3.291e+02 7.711e+01     0    30     0     0   791     0      0     1     0     0 0.000e+00 0.000e+00       <br><br>0  608372     0 9.598e-01 -4.609e+01 2.181e+02 4.68951501764343259281986e+00 4.892e-01 4.002e+02 1.912e+02 1.479e+02     0     3     0     0  1026     0      0     0     0     0 0.000e+00 0.000e+00<br><br>Could anyone give explainations for this??  Thank you very much.<br><div><br>Regards,<br>Hongwei <br></div><span style="font-weight: bold;"><br></span><div><br></div></div><br> </body></html>