[Rtk-users] R: Trying to reconstruct with a 180 degrees circular projection geometry

[Simon Rit]

Hi Clément,
To complement Gabriele's response and explains what goes on. FDK requires a
360° acquisition. RTK will calculate the angular gap between the current
projection and the two neighbors. With your configuration, two projections
take an angular weight (the delta when discretising the backprojection
integral) of about 90°.
You can do a short scan with Parker weightings but, as stated by Gabriele,
that necessitates at least 180° + the cone angle.
Simon

On Fri, Dec 11, 2020 at 9:23 AM <gabriele.belotti.bergamo at gmail.com> wrote:

> Hi Clément,
>
> It seems likely that your geometry is not 180+fan-angle complete and
> therefore cannot lead to a proper reconstruction. From your attached
> geometry, you sweep from 0 to 178° (180-increment).
>
> My suggestion would be to try some intermediate angles, so to recreate a
> complete ShortScan. I suggest you to try at least a 200/220 ° arc to check
> on your simulation pipeline.
>
> I hope this is helpful,
> Gabriele
>
>
>
> *Da:* Rtk-users <rtk-users-bounces at public.kitware.com> *Per conto di *Clément
> Mirabel
> *Inviato:* venerdì 11 dicembre 2020 09:11
> *A:* rtk-users at public.kitware.com
> *Oggetto:* [Rtk-users] Trying to reconstruct with a 180 degrees circular
> projection geometry
>
>
>
> Hi,
>
>
>
> I have been trying to set the geometry in ThreeDCircularProjectionGeometry
> with values between 0 and 180 degrees, to reproduce the motion of some
> acquisition systems, but reconstruction is far from the expected result
> when the gantry angle does not reach max value of (360-increment).
> (Attached is the geometry file generated)
>
> My workflow is the following :
>
>    - Apply JosephForwardProjectionImageFilter on a 3D Volume
>    - Try to reconstruct using FDKConeBeamReconstructionFilter
>
> Although, the result from JosephForwardProjectionImageFilter describes a
> 180 degrees rotation, the output of the reconstruction seems to display
> rays from opposite direction but not from rotated directions
>
>
>
> Here is a view of what is supposed to be an axial slice:
>
>
>
> Thanks for your help!
>
>
>
> Clément
>
>
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