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<p>Indeed the image is good !</p>
<p>And if you sum all slices of the left image, do you see rings with the 2.5mn scan ?</p>
<p><br>
</p>
<p>Did you include an energy threshold in GATE ? If yes, then did you include a readout module, and a which level ? In simulations, the main effect creating rings is usually due to events scattering at boundaries of block detectors leading to a loss of efficiency
in crystals at these boundaries.</p>
<p><br>
</p>
<p>As for the difference with STIR, I cannot tell that much. At least I can tell that in CASToR, the exact crystal positions are used for the reconstruction.</p>
<p>What projector did you use ? Also did you include an image-based PSF ? Because it can lessen the artifacts to some extent.</p>
<p><br>
</p>
<p>Simon</p>
<p><br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>De :</b> Sadek Nehmeh <san2028@med.cornell.edu><br>
<b>Envoyé :</b> lundi 14 septembre 2020 19:29<br>
<b>À :</b> STUTE Simon; castor-users@lists.castor-project.org<br>
<b>Objet :</b> RE: Normalization</font>
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<p class="MsoNormal"><span style="color:#1F497D">Many thanks Simon for your detailed response. Please see below an example transaxial slice and the summed coronal image for a 2.5 min of simulation. The images are artifact-free event though no normalization
correction was applied. I had to go with 30min of data to see the ring artifacts, even though very mild especially when compared to I am used to from STIR.
</span></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="color:#1F497D">Regards,</span></p>
<p class="MsoNormal"><span style="color:#1F497D">Sadek</span></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span></p>
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<p class="MsoNormal"><span style="color:#1F497D"><img id="Picture_x0020_1" style="width:4.4583in; height:2.0in" width="428" height="192" src="cid:image002.png@01D68A9B.07DF5890"></span><span style="color:#1F497D"></span></p>
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<p class="MsoNormal"><b>From:</b> STUTE Simon <simon.stute@chu-nantes.fr> <br>
<b>Sent:</b> Monday, September 14, 2020 5:26 AM<br>
<b>To:</b> Sadek Nehmeh <san2028@med.cornell.edu>; castor-users@lists.castor-project.org<br>
<b>Subject:</b> [EXTERNAL] RE: Normalization</p>
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<p><span style="font-family:"Calibri",sans-serif; color:black">Dear Sadek,</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black"> </span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black">The PET sensitivity image is computed using one of the three following method :</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black"> - if a histogram datafile is provided, then the sensitivity is computed by backward-projecting the product of attenuation and normalization corrections of each LOR of the datafile, one-the-fly
for each subset</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black"> - if a listmode datafile is provided, without normalization datafile, a double loop is performed over all crystals of the scanner so that for each possible crystal pair, the corresponding line
joining the two crystals is used to forward-project the attenuation image (if provided) and backward-project the corresponding attenuation coefficient factor in the sensitivity image. In that case, no scanner normalization is taken into account so that it
is implicitly assumed that all crystal pairs have the same efficiency</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black"> - if a listmode datafile is provided, a normalization datafile can be provided so that the sensitivity image will be computed from it. This normalization datafile contains all LORs that may detect
events, with associated attenuation and normalization coefficients. A loop is done over all these LORs and the coefficients are backward projected.</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black"> </span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black">Could you send an image that you reconstructed ?</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black"> </span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black">If you did not proceed to the simulation of a normalization scan (using a rotating source or a "donnut" source) in order to compute normalization coefficients and build a normalization datafile,
then it is very likely that you have artifacts in your image.</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black"> </span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black">Did you try to sum up all slices of the reconstructed image ? Do you have sufficient statistics in your dataset ?</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black"> </span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black">Best</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black">Simon</span></p>
<p><span style="font-family:"Calibri",sans-serif; color:black"> </span></p>
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<p class="MsoNormal"><b><span style="color:black">De :</span></b><span style="color:black"> Castor-users <<a href="mailto:castor-users-bounces@lists.castor-project.org">castor-users-bounces@lists.castor-project.org</a>> de la part de Sadek Nehmeh <<a href="mailto:san2028@med.cornell.edu">san2028@med.cornell.edu</a>><br>
<b>Envoyé :</b> vendredi 11 septembre 2020 18:26<br>
<b>À :</b> <a href="mailto:castor-users@lists.castor-project.org">castor-users@lists.castor-project.org</a><br>
<b>Objet :</b> [Castor-users] Normalization</span><span style="font-size:12.0pt; color:#212121">
</span></p>
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<p class="MsoNormal"><span style="color:#212121">Dear Castor Developers and Users,</span></p>
<p class="MsoNormal"><span style="color:#212121"> </span></p>
<p class="MsoNormal"><span style="color:#212121">I have successfully reconstructed the GATE images for a Biograph Vision. The images look great and artifact-free. The interesting thing is that even though I did not apply any normalization correction, the images
do not show any rings artifacts! Could someone please clarify some details about how the sensitivity image is produced and how the algorithm compensates for the expected ring artifacts?</span></p>
<p class="MsoNormal"><span style="color:#212121"> </span></p>
<p class="MsoNormal"><span style="color:#212121">Thanks,</span></p>
<p class="MsoNormal"><span style="color:#212121">Sadek</span></p>
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