<html><head></head><body><div style="font-family: Verdana;font-size: 12.0px;"><div>Hello,</div>
<div>thank you for the fast reply.</div>
<div>To answer your questions first.</div>
<div>In this case the abbrevation pcb stands for printed circuit board.</div>
<div>Next point is the trajectory we are currently handling with.</div>
<div>Please see the attached image "trajectory.png". There are two schematics showing the side view and top view for trajectory type 1</div>
<div>and a side-view for trajectory type 2.</div>
<div> </div>
<div>For type 1:</div>
<div>The xray source is fixed. The pcb is clamped within a transport, so the pcb and the detector are moveable with in the xy plane.</div>
<div>As you can see at the image, the pcb moves along a circular path but the pcb itself is not rotating. And let's assume that the iso ray</div>
<div>always passes through the centre of the pcb and the centre of the detector.</div>
<div> </div>
<div>For type 2:</div>
<div>The xray source is fixed and the detector is tilted. The pcb lies centred in the middle of a table. So that the pcb rotates around its centre</div>
<div>around the z-axis.</div>
<div> </div>
<div> </div>
<div>I hope this makes clear what trajectory i'm dealing with. Thank you.</div>
<div> </div>
<div>Kind regards,</div>
<div>Robert C.</div>
<div> </div>
<div> </div>
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<div style="margin:0 0 10px 0;"><b>Gesendet:</b> Dienstag, 10. Oktober 2017 um 15:31 Uhr<br/>
<b>Von:</b> "Cyril Mory" <cyril.mory@creatis.insa-lyon.fr><br/>
<b>An:</b> "Robert Calliess" <robert.calliess@gmx.de>, rtk-users@public.kitware.com<br/>
<b>Betreff:</b> Re: [Rtk-users] FDK for planar ct</div>
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<p>Dear Robert,</p>
<p>Your description of the trajectory is very obscure to me. Maybe you have a very unusual X-ray system. Could you make the following points clear :</p>
<p>- what is a PCB ?</p>
<p>- what is fixed/moving in your system (we need this information for the object, the source and the detector), and what kind of trajectories have the moving parts ?</p>
<p>- can you re-draw your sketch with just 2 or 3 positions (ideally, on similar but separate drawings), each one with the object, the source and the detector ?</p>
<p>If you do that, we should have a clear understanding of how your acquisition goes, and be able to give you appropriate advice.</p>
<p>Best regards,</p>
<p>Cyril</p>
<div class="moz-cite-prefix">On 10/10/2017 15:02, Robert Calliess wrote:</div>
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<p class="MsoNormal"><span>Hello rtk users,</span></p>
<p class="MsoNormal"><span>I have question to the RTK FDK Filter. As far as I understand from to the fourier slice theorem the object to be reconstructed needs a circular trajectory and needs to rotate its own centre.</span></p>
<p class="MsoNormal"><span>Please have a look at the attached sketch. With this planar trajectory (Object, a PCB, is moved on a circle trajectpry “in-plane”, PCB itself is not rotating) do I need</span></p>
<p class="MsoNormal"><span>a special filtering if I want to use FDK for planar CT with respect to the sketched trajectory ? I tried a circular in-plane trajectory where the PCB is centred and rotates</span></p>
<p class="MsoNormal"><span>around its centre point. And with 100 projections I get good results. But with the trajectory I described (sketch, attached image) the results are not so good.</span></p>
<p class="MsoNormal"><span>Because of the row-wise ramp filter It looks like there is a directional dependency. My assumption is, and with respect to fourier slice theorem, that the missing object</span></p>
<p class="MsoNormal"><span>rotation (rotation around itself) causes there directional effects.</span></p>
<p class="MsoNormal"><span> </span></p>
<p class="MsoNormal"><span>So my questions to the experts are. Do I need to apply a special filtering before backprojecting with FDK or is it just the wrong</span></p>
<p class="MsoNormal"><span>algorithm for this kind of trajectory ?</span></p>
<p class="MsoNormal"><span> </span></p>
<p class="MsoNormal"><span>kind regards,</span></p>
<p class="MsoNormal"><span>Robert C.</span></p>
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