[Rtk-users] Reconstruction geometry

[Simon Rit]

Hi Christian,
Thanks for the share. It was not clear to me that you had a 90° scan sorry.
FDK is not appropriate for such a 90° scan, it's meant for a full 360°
scan. rtkfdk tries to apply a short scan but Parker weighting is for
180°+fan-angle. So I'm not sure what to expect from FDK with such a scan.
The projections that you shared are 512x511, can you please clarify the
pixel size? I would try iterative reconstruction with such a scan.
Cheers,
Simon

On Fri, May 31, 2024 at 12:25 PM Christian Riesch <christian.riesch at live.com>
wrote:

> Hello Simon,
>
> Thanks for the quick response.
> So I have tried rtksimulatedgeometry with --arc 273 together with adding
> --neworigin=-153.5985,-153.2025,0 to rtkfdk.
> The result is different than before, but still looks very wrong (two
> ribbons and some vertical lines).
>
> I may be able to share some data later.
>
> Best regards,
> Christian
>
> ------------------------------
> *Von:* Simon Rit <simon.rit at creatis.insa-lyon.fr>
> *Gesendet:* Donnerstag, 30. Mai 2024 08:48
> *An:* Christian Riesch <christian.riesch at live.com>
> *Cc:* rtk-users at openrtk.org <rtk-users at openrtk.org>
> *Betreff:* Re: [Rtk-users] Reconstruction geometry
>
> Hi,
> I can see two problems:
> - you need to indicate the short scan to rtksimulatedgeometry, e.g. --arc
> 273 or, if the angle convention is opposite in your system, --arc -273. You
> may have to tune the --first_angle option to position the volume as you
> wish but that should not prevent accurate reconstruction.
> - you need to center your projections, i.e., add the option
> --neworigin=-153.5985,-153.2025,0 to rtkfdk, computed with
> -0.5*(3104-1)*0.099 and -0.5*(3096-1)*0.099.
> Don't hesitate to share a dataset if that does not help.
> Good luck!
> Simon
>
>
> On Thu, May 30, 2024 at 6:58 AM Christian Riesch <
> christian.riesch at live.com> wrote:
>
> Hello,
>
>
>
> I'm currently trying to use RTK for a reconstruction from a stack of
> images that resulted from a 90° scan, but struggling to get the parameters
> right.
>
> On the other hand, I was able to get what looks like a faithful
> reconstruction using the Astra toolbox and the script from
> https://tomroelandts.com/articles/astra-toolbox-tutorial-reconstruction-from-projection-images-part-1
>
>
>
> I have these parameters from the X-ray device that captured the images
> (size 3104x3096):
>
>             "fod_mm": 75.46, (focus to object distance)
>
>             "odd_mm": 407.07, (object to detector distance)
>
>             "pixel_size_mm": 0.099,
>
>             "start_arc_deg": 45.0,
>
>             "stop_arc_deg": -45.0
>
> (There is also "detector_offset_mm": 9.8, which I have ignored so far with
> both Astra and RTK.)
>
>
>
> So I have tried to create a geometry using
>
> .\rtksimulatedgeometry.exe -o"geo.xml" -n91 -f45 -a90 --sdd=482.53
> --sid=75.46
>
> where sdd = fod_mm + odd_mm and sid = fod_mm,
>
> and a reconstruction with
>
> .\rtkfdk.exe -p"images" -r".*tif" -g"geo.xml" -o"out.tif"
> --dimension=512,512,200 --newspacing=0.099
>
>
>
> However, out.tif contains mostly zeros and a weird ribbon-like shape in
> the center. So I think my geometry is wrong, but I don't know how to fix it.
>
>
>
> For comparison, here are the input parameters for the Astra script:
>
> distance_source_origin = 75.46  # [mm]
>
> distance_origin_detector = 407.07  # [mm]
>
> detector_pixel_size = 0.099 # [mm]
>
> num_projections = 91
>
> start_angle_deg = 45
>
> stop_angle_deg = 135
>
>
>
> Any pointers would be appreciated.
>
>
>
> Best regards,
>
> Christian Riesch
>
>
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