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

[Simon Rit]

Hi,
I have almost never worked with Varian data but it looks like a
geometry problem. Maybe the problem comes from a bad ordering of the
projections which results in assigning a bad geometry to each
projection. How did you name your projections? Maybe check that the
order matches that of the RTK geometry file. Otherwise, there might be
an issue in the creation of the geometry file itself.
All this sounds good, happy bug hunt and don't hesitate to share your
code when you feel it's ready.
Simon

On Tue, Sep 13, 2016 at 7:06 PM, Andreas Gravgaard Andersen
<andreasg at phys.au.dk> wrote:
> 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, XMLReader, GeometryReader]
>
> 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).
> 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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