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

[Simon Rit]

Hi Vincent,
RTK can parametrize any orientation of the detector with the three angles
GantryAngle, InPlaneAngle, OutOfPlaneAngle. 0.025° seems very small indeed!
I don't know how much you know about software B but the easiest would be to
have either the projection matrix or the source position, detector
position, u axis and v axis in patient/object coordinates to derive the RTK
parameters.
Good luck with this!
Simon

On Tue, May 10, 2022 at 5:23 PM Vincent Libertiaux <vl at xris.eu> wrote:

> On 25.04.22 09:07, Simon Rit wrote:
>
> 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
>> >
>> > _______________________________________________
>> > Rtk-users mailing list
>> > 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
>>
>> _______________________________________________
>> Rtk-users mailing list
>> Rtk-users at public.kitware.com
>> https://public.kitware.com/cgi-bin/mailman/listinfo/rtk-users
>>
>> Hi Simon, hi Jasper.
>
> I have investigated a bit more on that issue.  I told you in my first
> message that both software we used besides rtk found the same set of
> parameters.  After playing a bit more with the software "B" (the one that
> gives the sharp edges), I found out that the tilt angle is found to be 0
> and it is the out-of-plane angle around the vertical axis of the detector
> which is non zero (and very coincidentally is very close to the tilt angle
> we computed).  The value is quite low (0.025°).  I am a bit puzzled as, if
> I am not mistaken, the literature always assumes that both out of plane
> angles are negligible as long as they don't come close 2°.  We are two
> order of magnitude below this value, hence my surprise.
>
> I am also wondering if this angle can be introduced in the rtk geometry.
> From the doc (http://www.openrtk.org/Doxygen/DocGeo3D.html), it seems
> that only the out-of-plane angle around the detector horizontal axis is
> considered.  Is that correct ?  If yes, is there a way to model the other
> one with the available parameters ?
>
> Once again, thank you for any help you can provide.
>
> Kindest regards,
>
> Vincent
>
>
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://public.kitware.com/pipermail/rtk-users/attachments/20220510/9ad264be/attachment-0001.htm>