<html><head><meta http-equiv=Content-Type content="text/html; charset=utf-8"><META name="Author" content="Novell GroupWise WebAccess"></head><body style='font-family: Tahoma, sans-serif; font-size: 13px; '>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"><meta name="Author" content="Novell GroupWise WebAccess"><div><div><div><div><div><div>Hello all,<br><br></div>I've been checking
the relative sensitivity of a PET geometry by taking the ratio of true
events to total events. I checked this with both optical photons and
non-optical photon simulations and got significantly different results. I
am using LYSO as the scintillator and a small acrylic cube as a
phantom. The prevalence of Compton events in the phantom using the
attachPhantomSD was negligible compared to the crystal for both the
optical and non-optical simulations. I used a Na-22 source at the centre
of the FOV. <br><br></div>With optical processes on, I got a
sensitivity of about 90% (so 10% Compton) for 100,000 coincident events.
However without optical processes on, I got a sensitivity of about 35%
(65% Compton) for 1mil events. <br><br></div>The only differences in the
macro files are defining all the surfaces in the optical files and the
other unique optical commands. The geometries, physics lists, and
digitizers (minus opticaladder of course) were identical.<br><br></div>Where could this huge discrepancy be coming from? I appreciate any insight that anyone can give me.<br><br></div>Cheers,<br>Devin Van Elburg<br><br>------------------------<br class="">
Physics w/ c/ Biomedical Physics<br class="">
Lakehead University<br></div></body></html>