Hi,<br><br>I think that it is the case for random coincidences. Check if there are others coincidences that have the same XYZ position for both singles. If you are simulating the PETbenchmark, you would have about 3,3% of random coincidences, but if you have modeled your own scanner, maybe you put to much activity or a too big time window in your coincidence sorter, and so you will get a huge random coincidences percentage. <br><br>Hope it helps,<br>Simon<br><br><div><span class="gmail_quote">2007/11/19, 周凤银 <<a href="mailto:fengyin0629@gmail.com">fengyin0629@gmail.com</a>>:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> <div>Dear everyone:</div> <div>       I an simulating the PET machine by gate. When I see the gateCoincidences.dat, I find that the XYZ position of the annihilation in world referential in first single is different from the second single. I think the XYZ position of the annihilation should be same. I do not know why. I really hope there be someone can reply the question. </div> <div>       Thank you very much！<span style="font-size: 9.5pt; font-family: Arial;" lang="EN-US"><br><br></span></div> <br>_______________________________________________<br>Gate-users mailing list<br><a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:Gate-users@lists.healthgrid.org">Gate-users@lists.healthgrid.org</a> <br><a onclick="return top.js.OpenExtLink(window,event,this)" href="http://lists.healthgrid.org/mailman/listinfo/gate-users" target="_blank">http://lists.healthgrid.org/mailman/listinfo/gate-users</a><br><br></blockquote> </div><br>