[Rtk-users] RTK simulating projection from defined object (Shepp Logan like txt file) issue

[Pavel Kudrna]

Hi,

I am prety new to RTK, but through I am learning with it I found a issue the is not clear to me. I followed the procedure from http://wiki.openrtk.org/index.php/RTK/Scripts/3DCG where I changed few things:

1) I simplified the Shepp Logan file to just simple sphere (in attachement).
2) I generated projections (using output_xml.xml – two whole gantry rotation in two diffferent y offsets) – the xml has been generated via python script (most of it-in attachment) which is reproducing procedure described in http://www.openrtk.org/Doxygen/DocGeo3D.html
3) Then I looked at the projections.mha in VolView (too large to send, please see the screenshot bellow)

My questions are 2:

1) Why there is a shift in Y-Z quadrant in generated projections.mha? It should be perfectly alligned – two of my colleagues has been so kind to check the procedure for me and found no mistake (the sinogram of sphere in the zero position(x=y=z=0) should be symetric perfectly) – what I am doing wrong?
2) I simulated corrected projection byte by byte (into MHA) and then tried to use back-projection  (rtkfdk) and Sart (rtksart)-you can see in output_xml.xml that the gantry angle is linear (not between -180° and 180° or between 0° and 360°), because when I put it into -180° and 180° it didn’t reconstruct anything properly – why is it? It is not possible to use same angle value more then once in xml geometry file (even if it has different y shift of detector and source)?

Purpose of this testing is that I am going to reconstruct data from helical CT, but my first attemattempt failed and I am going step by step to find out hat is wrong in my procedure.

I use docker version of RTK given by http://wiki.openrtk.org/index.php/RTK_wiki_help

Thank you…

Kind regards…

p.



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