<div dir="ltr">Hi Maxime,<div><br></div><div>Could you remember the name of the paper you mentioned? I am interested in that paper. Thanks!</div><div><br></div><div>Best,</div><div>Xinjie</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Apr 23, 2021 at 2:05 PM Maxime Toussaint <<a href="mailto:Maxime.Toussaint@usherbrooke.ca">Maxime.Toussaint@usherbrooke.ca</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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Greetings,</div>
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<span>The profiles remind me of a nice paper that studied the consequences of over/under estimation of the TOF kernel.</span> Since you use GATE, is it possible that you have made a slight error in setting the TOF resolution? The command in GATE "/gate/digitizer/Singles/timeResolution/setTimeResolution
X" defines the <b>single</b> resolution as X. As such, the <b>coincidence</b> resolution is sqrt(2) * X.
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Note: My memory tells me that CASTOR extract the coincidence TOF resolution directly from the .mac, so this should not happen. However, you "set it by hand", which makes it a possibility.</div>
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Bests,</div>
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Maxime Toussaint</div>
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<div id="gmail-m_9008221171331512401divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>De :</b> Castor-users <<a href="mailto:castor-users-bounces@lists.castor-project.org" target="_blank">castor-users-bounces@lists.castor-project.org</a>> de la part de Philip Kalaitzidis <<a href="mailto:kalaitzidis.philip@gmail.com" target="_blank">kalaitzidis.philip@gmail.com</a>><br>
<b>Envoyé :</b> 23 avril 2021 12:54<br>
<b>À :</b> <a href="mailto:castor-users@lists.castor-project.org" target="_blank">castor-users@lists.castor-project.org</a> <<a href="mailto:castor-users@lists.castor-project.org" target="_blank">castor-users@lists.castor-project.org</a>><br>
<b>Objet :</b> [Castor-users] CASToR TOF reconstruction</font>
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<span lang="EN-US">Dear CASToR developers and users,<span></span></span></p>
<p style="margin:0in 0in 8pt;line-height:107%;font-size:11pt;font-family:Calibri,sans-serif">
<span lang="EN-US">I have a question regarding an issue with CASToR TOF reconstruction.<span></span></span></p>
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<span lang="EN-US">I will give a brief background of the issue: I have modelled the G.E. Discovery MI (DMI) PET/CT with GATE and simulated a PET acquisition with the NEMA IQ phantom. I have converted the data to the CASToR list-mode format and so far, there
are generally no problems. However, when including TOF in the data file I get an increased signal in the reconstructed image in places where I do not expect, e.g., in the lung insertion, but also a quite reduced signal in the spheres.
<span></span></span></p>
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<span lang="EN-US">The TOF information for each event that I write to the binary file I simply take the arrival time difference between crystal1 and crystal2, i.e., time1-time2 and then multiply the difference by 1e+12 to get the delta time in ps. I then save
the crystals in the binary file as Crystal ID1 (c1) corresponding to GATE crystal1 and Crystal ID2 (c2) corresponding to GATE crystal2 (since it is mentioned in the general documentation that the TOF delta time is positive when the emission occurs closer to
c2.) In the header file I set the TOF resolution to 380 ps and the TOF measurement range to 4900 ps. I decided to only write the true coincidences in the binary file (together with attenuation, normalization, and the inclusion of a span of 2 for indirect slices
for segment 0) so that I could efficiently look at the effect of TOF without having to bother with random- and scatter correction.
<span></span></span></p>
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<span lang="EN-US">If I then reconstruct the data, I notice an increased signal in the insertion compartment, as well as a notable reduction in signal between some of the spheres (especially visible between the largest spheres), as opposed to if I reconstruct
the data using the <i>-ignore-TOF </i>option (or without including TOF information in neither the binary- nor the header file.) If I reconstruct the same data but increase the TOF resolution to, e.g., 700 ps, the signal in the insertion compartment is reduced
and the reduced signal between spheres are no longer present. (I also tested using the GATERootToCastor converter with the TOF resolution to 380 ps yielding similar results.)<span></span></span></p>
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<span lang="EN-US">I have attached images showing a slice of the three examples that I mentioned (TOF included with 380 ps TOF resolution, TOF included with 700 ps TOF resolution, and with the
<i>-ignore-TOF </i>option used.) I have also included profiles through the same slices passing through two of the spheres and the insertion compartment.<span></span></span></p>
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<span lang="EN-US">Intuitively, this seems to yield erroneous results (with 380 ps TOF resolution), but I cannot seem to understand why this effect occurs. I was hoping someone could help me understand what the issue might be, if I have missed something, or
whether I am on the wrong track and have misunderstood the <i>“TOF-induced”</i> results.<span></span></span></p>
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<span lang="EN-US">I hope to hear from you.<span></span></span></p>
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<span lang="EN-US">Best regards,<br>
<i>Philip</i><span></span></span></p>
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<a href="https://castor-project.org/mailing-list" rel="noreferrer" target="_blank">https://castor-project.org/mailing-list</a></blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><b><font color="#000000">....................................................</font></b><br></div><div><b><span style="color:rgb(153,0,0);font-family:"arial black",sans-serif;font-size:x-small">Xinjie Cao</span></b><br></div><div><b><font size="1" face="arial black, sans-serif">M.Eng. / Ph.D. Candidate</font></b></div><div><b><font size="1" face="arial black, sans-serif">Research Project Assistant</font></b></div><div><b><font size="1" face="arial black, sans-serif">Department of Electrical and Computer Engineering & Radiology </font></b></div><div><b><font size="1" face="arial black, sans-serif">Novel Medical Imaging Technologies Lab</font></b></div><div><b><font size="1" face="arial black, sans-serif">Health Science Center Level 8</font></b></div><div><b><font size="1" face="arial black, sans-serif">Stony Brook, NY 11794-8460 </font></b></div><div><b><font size="1" face="arial black, sans-serif">Tel: +1 (631)202-9445</font></b></div><div><a href="https://you.stonybrook.edu/goldan/people/" target="_blank">you.stonybrook.edu/goldan/people/</a><b><font size="1" face="arial black, sans-serif"><br></font></b></div><div><font size="1" face="arial black, sans-serif"><b>email: </b><a href="mailto:xinjie.cao@stonybrook.edu" target="_blank"><b>xinjie.cao@stonybroo</b>k.edu</a></font></div><div><font size="1" face="arial black, sans-serif"><br></font></div><div><font size="1" face="arial black, sans-serif"> </font><img src="https://docs.google.com/uc?export=download&id=12iMPAuaMtpKRdkcmBleVsP6iWiM4wlm_&revid=0B_TLWOu4jP1eWnFFRW9qQXlicTY3ZTVzWnR5QkRVY3RRT3JVPQ" width="200" height="28"> <img src="https://drive.google.com/a/stonybrook.edu/uc?id=17TB1Ha3enD8HC5e_Ez238vpeBF92aCgH&export=download" width="200" height="33"></div><div><div><b><font color="#000000">....................................................</font></b></div></div></div></div></div></div></div></div></div></div></div></div></div>