<!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 6.5.7651.59"> <TITLE>RE: [Gate-users] Photons on a ring surface, new detector implementation and readout and new time management</TITLE> </HEAD> <BODY>  Hi, Miguel, Nice questions. I would provide you my opinion on your first question. First, let me ask you a question. What is the material you used in your 0.1mm thick crystal? If it is a *NORMAL* (e.g., GSO) crystal, of course we should expect a little edep in this thin layer. Instead, you can describe a virtual material with very large density,, letting photons be stopped completely within one step in this thin layer. Then you can figure out what are those photon's position, momentum from hit file.  Another way is to modify GateSteppingFunction (correct name?) and let a track be killed when it reaches crystalSD. My two cents. Hope it helps. Yu Chen, Ph.D. University of Massachusetts Medical School Division of Nuclear Medicine 55 Lake Avenue North Worcester, MA 01655-0243 Phone:  (508) 856-6123 Fax:    (508) 856-4572 -----Original Message----- From: gate-users-bounces@lists.healthgrid.org on behalf of Miguel Couceiro Sent: Sun 4/29/2007 7:41 PM To: Gate-users@lists.healthgrid.org Subject: [Gate-users] Photons on a ring surface, new detector implementation and readout and new time management Hi all! Is there any way to use GATE to simulate the interaction of photons within phantoms and propagate them to the surface of an annulus, and then save the information needed to continue the simulation in Geant4? This is easy to do in Geant4, but I would like to use voxelized phantoms. I have tried to define a cylindricalPET whith 0.1 mm thick, and disable the module, submodule, etc., and attach the crystalSD to the cylindricalPET. However, the edep of the Hits file is very low, as expected, and there is no information on photon momentum to proceed the simulation in Geant4. Do you think that creating another sensitive detector, for instance the cylindricalSD, and getting the pre-step point information would solve the problem? Another possibility is to implement in GATE the detector that I want to simulate (not crystal based). This means to implement, at least, a new system and readout. Were can I find enough information to do this? My last question concerns the Time Management. Sometimes we perform a complete simulation with only one isotope, with the correct digitizer sequence. Then we want to change the activity, for instance to study the count rate performance. Since digigate is must faster then a complete simulation, we could benefit if instead of a single time stamp for singles there was three time stamps: one for positron annihilation, one for photon interaction in the detector after annihilation, and one that would be the sum of the two. This first one could be changed by the digitizer based on the source activity, and last one could be calculated based on the first and second ones. Is there any way to use this approach in digigate? Thanks in advance for your answers, Miguel _______________________________________________ Gate-users mailing list Gate-users@lists.healthgrid.org <A HREF="http://lists.healthgrid.org/mailman/listinfo/gate-users">http://lists.healthgrid.org/mailman/listinfo/gate-users</A> </BODY> </HTML>