<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Dear GATE users and developers,<div><br></div><div>I have noticed a strange behavior with PET simulations that use low counts and short time slices. In my set-up, I am simulating a point source inside the Inveon PET scanner. The activity of the point source is varied from 1 to 1000 Bq,the total run time is 100 sec, the the time slice is 0.2 s (so 500 slices).</div><div><br></div><div>For 1 Bq, one would expect ~ 7 counts on average but in fact I observed 23 (average over 250 realizations). For higher activity, the error is smaller but still statistically significant (see attached plot). The issue disappears around 1000 Bq or if the number of time slices is reduced to ~ 10 (instead of 500). Note that if the activity of the source is 0 Bq, then no counts are observed, so this is not a background issue.</div><div><br></div><div>So my question is is there an explanation for this behavior, or could this be a bug in how counts are generated within each time frame?</div><div><br></div><div>Thank you for your help in solving this issue.</div><div><br></div><div><div apple-content-edited="true">
<div style="color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div style="color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Guillem Pratx, PhD<br>_______________________________________________<br><br> Assistant Professor<span class="Apple-tab-span" style="white-space: pre;"> </span>Office A247<br> Radiation Oncology<span class="Apple-tab-span" style="white-space: pre;"> </span>1050 Arastradero Rd<br> Stanford University<span class="Apple-tab-span" style="white-space: pre;"> </span> Palo Alto, CA 94304<br> <a href="http://pratxlab.stanford.edu">http://pratxlab.stanford.edu</a> (650) 724-9829<br>_______________________________________________</div></div>
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