Hi Anayisse, Maybe you have a too low activity, for a too big attenuation map ?? Because there is no command that permits you to filter out your random coincidences. Simon <div> 2007/12/10, anayisse arnaud <<a href="mailto:anayisse_arnaud@hotmail.com">anayisse_arnaud@hotmail.com</a>>:<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Dear Gate users, I simulated a PET scanner, I used only the command line : /gate/digitizer/Coincidences/setWindow 10. ns ,  for coincidence sorting. When I compared the two singles event IDs in the coincidences file, I found that the IDs are identical for each coincidence event ! It means that there are no Random coincidences ? but I don't understand this result because i didn't use any other command to filter out the Random coincidences ? What do you think please? I would be grateful if anyone could explain to me the reason ? Best Regards Anayisse _________________________________________________________________ Connect to the next generation of MSN Messenger <a href="http://imagine-msn.com/messenger/launch80/default.aspx?locale=en-us&source=wlmailtagline_______________________________________________">http://imagine-msn.com/messenger/launch80/default.aspx?locale=en-us&source=wlmailtagline_______________________________________________ </a> Gate-users mailing list <a href="mailto:Gate-users@lists.healthgrid.org">Gate-users@lists.healthgrid.org</a> <a href="http://lists.healthgrid.org/mailman/listinfo/gate-users">http://lists.healthgrid.org/mailman/listinfo/gate-users </a> </blockquote></div>