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Hi Luca,
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<div class="">Thank you for your response. I found no true events in the delayed window data. The delayed offset is 200ns so this makes sense to me. I had not thought about the multiple coincidences policy, I do not set it in my macros and therefore I think
it is the default “keepIfAllAreGoods”. This would be the case for both the Coincidence data and Delayed and so I would not expect a difference.</div>
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<div class="">I also noticed the broken link in the original email, here is the updated:
<a href="https://github.com/UCL/STIR-GATE-Connection/blob/master/ExampleScanners/D690/digitiser_D690.mac#L39-L54" class="">
https://github.com/UCL/STIR-GATE-Connection/blob/master/ExampleScanners/D690/digitiser_D690.mac#L39-L54</a></div>
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<div class="">Robert<br class="">
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<div class="">On 14 Apr 2021, at 03:56, PRESOTTO LUCA <<a href="mailto:presotto.luca@hsr.it" class="">presotto.luca@hsr.it</a>> wrote:</div>
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<div class="">Hi,<br class="">
Not really sure, I'm just guessing. I'm not using delayed window as our clinical scanners correct randoms using single rates.<br class="">
I'm wondering 2 options, both related to the count-rate. Is it possible that your delayed window might contain some true coincidences? Also, which is your multiple coincidences policy?<br class="">
<br class="">
Luca<br class="">
<br class="">
________________________________________<br class="">
Da: Gate-users <<a href="mailto:gate-users-bounces@lists.opengatecollaboration.org" class="">gate-users-bounces@lists.opengatecollaboration.org</a>> per conto di Twyman, Robert <<a href="mailto:robert.twyman.18@ucl.ac.uk" class="">robert.twyman.18@ucl.ac.uk</a>><br class="">
Inviato: martedì 13 aprile 2021 19:03<br class="">
A: <a href="mailto:Gate-users@lists.opengatecollaboration.org" class="">Gate-users@lists.opengatecollaboration.org</a><br class="">
Oggetto: [Gate-users] Greater number of delayed coincidences than random coincidences for PET data<br class="">
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Dear GATE users,<br class="">
<br class="">
I have been simulating PET acquisitions using GATE on an XCAT phantom for reconstruction using STIR. The reconstruction processes is iterative and therefore I have need to estimate the contributions due to Random and Scattered events in the measured data. I
am estimating the Randoms from the Delayed coincidence data output by GATE using a 200ns Delayed offset. Both the Coincidence and Delayed windows are set to 4.9ns.<br class="">
<br class="">
Please see my digitiser on GitHub: <a href="https://github.com/UCL/STIR-GATE-Connection/blob/master/ExampleScanners/D690/digitiser_D690https://github.com/UCL/STIR-GATE-Connection/blob/master/ExampleScanners/D690/digitiser_D690.mac#L39-L54" class="">
https://github.com/UCL/STIR-GATE-Connection/blob/master/ExampleScanners/D690/digitiser_D690https://github.com/UCL/STIR-GATE-Connection/blob/master/ExampleScanners/D690/digitiser_D690.mac#L39-L54</a><br class="">
.mac#L39-L54<br class="">
<br class="">
The problem is as follows. I unlist (using STIR) all valid events in the Delayed ROOT file. I unlist all random events (defined as the photons having different eventIDs) from the Coincidence ROOT file. The result is, ~10% more events in the Delayed data, which
has knock on effects to my Randoms estimation and into the Scatter estimation…<br class="">
<br class="">
Does anyone have any idea why I might have more events in my Delayed data than Random events in my Coincidence data?<br class="">
<br class="">
Regards,<br class="">
Robert Twyman<br class="">
Ph.D Student<br class="">
UCL<br class="">
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Rispetta l’ambiente: non stampare questa mail se non è necessario.<br class="">
Respect the environment: print this email only if necessary.<br class="">
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