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

[Vincent Libertiaux]

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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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