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<p>Hi Maggie,</p>
<p><br>
</p>
<p>The histogram is your sinogram but in the CASToR format. One histogram bin contains the number of detected counts in a given sinogram bin which is defined by a projection ID and a pixel ID.</p>
<p><br>
</p>
<p>The blank scan calibrate your couple source/detector.</p>
<p>You do a simulation without anything in the field of view for a single projection. You need that to know what is the expected number of counts without object.</p>
<p><br>
</p>
<p>Best<br>
</p>
<p>Simon<br>
</p>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>De :</b> Margarete Kattau <margarete.kattau@icr.ac.uk><br>
<b>Envoyé :</b> jeudi 19 mai 2022 16:12<br>
<b>À :</b> STUTE Simon; castor-users@lists.castor-project.org<br>
<b>Objet :</b> Re: Unexpected error when reconstructing CT image</font>
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Dear Simon,</div>
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<br>
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Thanks for your reply. I am not sure how to produce the histogram and am a bit confused about what each histogram bin contains. Is it the number of events along the width of the detector (so the pixels being the bins)? For my analysis, I reconstruct the individual
projection images and based on these, I build the sinogram, but I am not sure how to retrieve the histogram.</div>
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Also, could you please explain why I need a blank scan?</div>
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<br>
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Many thanks,</div>
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Maggie</div>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> STUTE Simon <simon.stute@chu-nantes.fr><br>
<b>Sent:</b> 18 May 2022 11:29<br>
<b>To:</b> Margarete Kattau <margarete.kattau@icr.ac.uk>; castor-users@lists.castor-project.org <castor-users@lists.castor-project.org><br>
<b>Subject:</b> RE: Unexpected error when reconstructing CT image</font>
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<p>Dear Margarete,</p>
<p><br>
</p>
<p>CASToR does not handle list-mode CT data for now as there is no algorithm able to deal with such data. The "Unknown event mode" is coming from that.<br>
</p>
<p><br>
</p>
<p>You will have to compute projections for each angle position of your phantom/scanner and then build a CT histogram datafile. You need to simulate a blank scan as well.<br>
</p>
<p><br>
</p>
<p>The CDF file is in a binary format, as opposed to the ascii format.</p>
<p><br>
</p>
<p>All mandatory and optional fields for each histogram bin (called generic event in castor) of the datafile are detailed in the documentation.</p>
<p><br>
</p>
<p>Best</p>
<p>Simon<br>
</p>
<p><br>
</p>
<p><br>
</p>
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<div id="x_divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>De :</b> Castor-users <castor-users-bounces@lists.castor-project.org> de la part de Margarete Kattau <margarete.kattau@icr.ac.uk><br>
<b>Envoyé :</b> mercredi 18 mai 2022 11:35<br>
<b>À :</b> castor-users@lists.castor-project.org<br>
<b>Objet :</b> [Castor-users] Unexpected error when reconstructing CT image</font>
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Dear CASToR users,</div>
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<br>
</div>
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I would like to reconstruct an image simulated using GATE. I've defined a detector, a fan-beam X-ray source and a simple phantom (water disc with a bone disc inside). The phantom is rotating around its axis so I can get a CT image. I've given CASToR the cdh
and cdf file (cdf and geom file attached). I have two questions:</div>
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<ol>
<li><span>Somehow CASToR initialises the image dimensions as (180,180,240), but they should be (240,180,0). What am I doing wrong?</span></li><li><span>At the end it says "Unknown event mode". I assume this is because of my cdf file? I wasn't sure how to format it exactly. It's too big to attach, but I am posintg the first few lines below. First column is the time, second is projection ID and the
third is pixel ID and each line corresponds to one event.</span></li></ol>
<div><span>0 2 31563
<div>0 2 21542</div>
<div>0 2 21680</div>
<div>0 2 21407</div>
<div>0 2 21721</div>
<div>0 2 21630</div>
<div>0 2 21450</div>
<div>0 2 21833</div>
<div>0 2 21645</div>
<div>0 2 21428</div>
0 2 7364</span></div>
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Has anyone an idea what I need to change?</div>
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<br>
</div>
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Many thanks in advance!</div>
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Best wishes,</div>
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Maggie</div>
<p>The Institute of Cancer Research: Royal Cancer Hospital, a charitable Company Limited by Guarantee, Registered in England under Company No. 534147 with its Registered Office at 123 Old Brompton Road, London SW7 3RP.
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