[Rtk-users] Lateral blur in a FDK reconstructed volume

[Simon Rit]

Hi Vincent (and Jasper),
I agree with Jasper that this is most likely due to a difference in
geometric calibration between the two datasets. Do you have more
information on what does B use (projection matrices, detailed
parametrization, etc.)? I think that such a blur can be caused by a
difference in source to detector distance (or, equivalently, detector pixel
size).
Simon

On Tue, Apr 19, 2022 at 11:08 AM Vincent Libertiaux <vl at xris.eu> wrote:

> On 16.04.22 13:52, Jasper Albertus Nijkamp wrote:
> > Hi Vincent,
> >
> >  From just these two images, it is a bit hard to help. However, I have
> seen similar challenges when the detector vertical offset is not properly
> set. If you could share a bit more data (fx projection data and the
> geometry), more people might be able to help.
> >
> > Jasper
> >
> > -----Original Message-----
> > From: Rtk-users <rtk-users-bounces at public.kitware.com> On Behalf Of
> Vincent Libertiaux
> > Sent: Friday, 15 April 2022 17:15
> > To: rtk-users <rtk-users at public.kitware.com>
> > Cc: Damien Koch <dk at xris.eu>
> > Subject: [Rtk-users] Lateral blur in a FDK reconstructed volume
> >
> > Hello rtk users !
> >
> > I am facing a problem for which I have exhausted all the possibilities
> except asking you.
> > I have performed a standard FDK reconstruction of a lego bricks
> assembly.  I used a custom-made code to compute the detector horizontal
> offset and tilt angle, found to be 1.15 mm and 0.02° respectively.  The
> result of the reconstruction is shown in the picture
> > https://ibb.co/LdMzJF2 .  The volume looks mostly sharp, except on the
> lateral edges, let's say on the last half brick.
> >
> > We had the opportunity to have the same volume reconstructed with two
> commercial solutions.  The first one, "A", produced the same results than
> rtk.  The second, "B", produced the result shown in the picture
> https://ibb.co/VwXMmRH
> >
> > In this case, the edges are sharp too.  The offset values found with
> this software were very close (1.13mm and 0.025° respectively) and feeding
> them to rtksimulatedgeometry didn't change my result.  No other correction
> was allegedly applied.
> >
> > I thought that the edge blurring was due to a wobbling artefact but it
> can't be the case according to the result with the "B" software.
> >
> > Do you have any idea on what could cause this blurring on the edges ?
> >
> > I thank you very much for any clue.
> >
> > Best regards,
> >
> > Vincent
> >
> > _______________________________________________
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> > Rtk-users at public.kitware.com
> > https://public.kitware.com/cgi-bin/mailman/listinfo/rtk-users
>
> Hi Jasper,
>
> thank you for your reply. I had already tried to play with the vertical
> offset but setting it to a value different than 0 progressively decrease
> the overall quality of the reconstruction.
> Following your advice, here are the projections:
>
> http://share.xris.eu/d91b09673bba
>
> word of warning, the set is very large (900 projections on a 3072x3072
> pixels detector, approx. size = 16Go)  I could try and make it smaller
> by downsampling it but I am afraid it would mask the problem.  I can try
> and do it on request.
> The geometric parameters I used were: SDD = 810 mm, SID = 410 mm,
> proj_iso_x = 1.15mm and in_angle = 0.02°.
>
>
> Best regards,
>
> Vincent
>
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>
>
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