<div dir="ltr"><div>Hi, </div><div>If you plot only the non-random coincidences, I think you will have a symmetric peak. </div><div>The asymmetric flat part of the profile probably comes from the random coincidences. </div><div>With Monte Carlo simulations, the particles are tracked one by one. All gammas contributing to an open coincidence window are buffered following their track order. So for two gammas coming from the same annihilation, the arrival time of the first tracked particle can be after the second tracked particle and vice-versa. </div><div>But for random coincidences, most of the time, the arrival time of the first gamma will be before the arrival time of the second gamma, which explains the asymmetric profile you get. </div><div>I think that you just have to randomize the order of the two gammas in each coincidence to get a symmetric profile. </div><div>Regards, Simon </div></div><div class="gmail_extra"> <div class="gmail_quote">On Tue, Aug 26, 2014 at 8:49 AM, 주요한 <<a href="mailto:yhjoo@gachon.ac.kr" target="_blank">yhjoo@gachon.ac.kr</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div link="blue" vlink="purple" lang="KO"><div>Dear Gate users. I create a new PET system follows the Gate user manual. (my gate version is 6.2) Actually I try to do the simulation with point source, the result image shows a point also. And sinogram is also good. However, the time difference histogram is not common things. I attached it as image files in this e-mail. In real system, the random part of time histogram has a symmetry distribution. However it has asymmetry distribution in the simulation. Which part makes this? If you know or guess, please let me know. I want to fix it. Here is associated script.. Thank you. /gate/digitizer/Singles/insert timeResolution /gate/digitizer/Singles/timeResolution/setTimeResolution 2.1 ns /gate/digitizer/Singles/insert deadtime/gate/digitizer/Singles/deadtime/setDeadTime 3000000. ps /gate/digitizer/Singles/deadtime/setMode nonparalysable/gate/digitizer/Singles/deadtime/chooseDTVolume level1 /gate/digitizer/name Coincidences /gate/digitizer/insert coincidenceSorter/gate/digitizer/Coincidences/setInputName Singles /gate/digitizer/Coincidences/setWindow 20. ns/gate/digitizer/Coincidences/setOffset 0. ns /gate/digitizer/Coincidences/describe /gate/digitizer/name delay/gate/digitizer/insert coincidenceSorter /gate/digitizer/delay/setWindow 20. ns/gate/digitizer/delay/setOffset 500. ns /gate/digitizer/delay/describe /gate/digitizer/name finalCoinc /gate/digitizer/insert coincidenceChain/gate/digitizer/finalCoinc/addInputName delay /gate/digitizer/finalCoinc/addInputName Coincidences/gate/digitizer/finalCoinc/usePriority true /gate/digitizer/finalCoinc/describe Best Regards,Yohan </div> <img src="http://mail.gachon.ac.kr:80/historySent.ds?act=confirm&sender=eWhqb29AZ2FjaG9uLmFjLmty&receiver=PGdhdGUtdXNlcnNAbGlzdHMub3BlbmdhdGVjb2xsYWJvcmF0aW9uLm9yZz4%3d&subject=V2h5IHRoZSB0aW1lIGRpZmZlcmVuY2UgaGFzIGFzeW1tZXRyeSBzaGFwZT8%3d&msgid=NjA1MTc2MjM3NDk2ODM2MjM0OA%3d%3d" height="0" width="0"> </div> _______________________________________________ Gate-users mailing list <a href="mailto:Gate-users@lists.opengatecollaboration.org">Gate-users@lists.opengatecollaboration.org</a> <a href="http://lists.opengatecollaboration.org/mailman/listinfo/gate-users" target="_blank">http://lists.opengatecollaboration.org/mailman/listinfo/gate-users</a> </blockquote></div> </div>