<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> <HTML> <HEAD> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <META NAME="Generator" CONTENT="MS Exchange Server version 6.5.7652.24"> <TITLE>RE: [Gate-users] 2 Head PET</TITLE> </HEAD> <BODY>  Hello José,    If 2 singles are found within your time cincidence window, they have to valid another condition which is the difference between their sector number (defautl value is 2). If your singles are defined at the level of your head detector, and because you have only 2 head, this condition is never achieved. You should change this defautl value and try /gate/digitizer/Coincidences/minSectorDifference 0 hope this help, bye sophie ------------------------- Sophie Kerhoas-Cavata DSM/DAPNIA/SphN tel:+33 1 69 08 33 68 mel: sophie.cavata@cea.fr -----Original Message----- From: gate-users-bounces@lists.healthgrid.org on behalf of José Ramos Sent: Tue 5/6/2008 9:49 PM To: gate-users@lists.healthgrid.org Subject: [Gate-users] 2 Head PET Dear GATE users: Actually I'm try to simulate a two head PET for small animals, I'm using an array of 20x20 crystals with dimensions 2.4x2.4x10mm3, the distance between the opposite detector heads is 80mm and the septal distance is 0.2mm. My problem is that I can't obtain coincidences, my coincidence time window is 10 ns and the source is F18 e+. Does anybody what's happen? Best regards </BODY> </HTML>