[Rtk-users] Fwd: Have you encountered this artifact?

[Andreas Gravgaard Andersen]

Dear RTK experts,

I am reconstructing Varian ProBeam projections of the Xim image format. I
have written the reader myself - very similar to the Hnd one already
available with RTK.
Links to my fork: [XimReader
<https://github.com/agravgaard/RTK/blob/master/code/rtkXimImageIO.cxx>,
XMLReader
<https://github.com/agravgaard/RTK/blob/master/code/rtkVarianProBeamXMLFileReader.cxx>,
GeometryReader
<https://github.com/agravgaard/RTK/blob/master/code/rtkVarianProBeamGeometryReader.cxx>
]

The reader apparently works (Images and angles displays as expected in UI),
however when reconstructing with a regular FDK* I get a reconstructed image
that is smeared out around the high and low density areas *[see attached
image]

I'm using half arc, full fan images with no bow-tie filter from Scripps
(~520 projections). Fixed detector and source (offset=0) with SID=2m,
SDD=3m.

*For the Hnd projections the reconstruction works perfectly (Same algorithm
<https://github.com/agravgaard/cbctrecon/blob/master/cbctrecon.cpp#L2726>).*
The reconstruction of the Xim projections performed on Varian software
works perfectly.

Without the Parker Short Scan Filter the first and last projections creates
streaks across the reconstruction as if they were way too bright.
If the first few projections are excluded, the following projection will
act the same way.

The projections are corrected for beam hardening and all the projections
have the expected attenuation.
No "smearing" filters (like median) is used, and iterative reconstruction
makes the same artifacts.

Setting the value of the first and last projection to zero has the same
effect as excluding. Changing the ramp filter only changes noise, not the
artifacts.

*Have any of you had a similar problem? *Am I missing something?
Any suggestions are welcome I'm running out of ideas.

Best regards
Andreas

__________________________________

Andreas Gravgaard Andersen

Department of Oncology,

Aarhus University Hospital

Nørrebrogade 44,

8000, Aarhus C

Mail:     andreasg at phys.au.dk

Cell:      +45 3165 8140
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