Hello,
the object is moving on a circular path. There are arrows between the
different detector positions showing the
moving direction. The source is static.
Kind regards,
Robert
*Gesendet:* Dienstag, 24. Oktober 2017 um 16:47 Uhr
*Von:* "Simon Rit" <[email protected]>
*An:* "Robert Calließ" <[email protected]>
*Cc:* "[email protected]" <[email protected]>
*Betreff:* Re: Re: [Rtk-users] FDK for planar ct
Hi,
I see one drawing only, not two. And the object does not seem to be
moving on your drawing, is it? If not and the source is also static
(as it seem), this is equivalent to one large projection.
Simon
On Tue, Oct 24, 2017 at 3:58 PM, "Robert Calließ"
<[email protected] <mailto:[email protected]>> wrote:
Hello,
I suppose there are still misunderstandings with respect to the
trajectory.
Attached you can find the two difference trajectories. I also had
a closer look to
the off centered fdk ( the paper you suggested). But I don't think
it is in my case.
The iso ray passes object center and detector center at each view.
Off centered fdk
has a different preweighting scheme.
You said that the RTK ramp filter is along the u axis (orthogonal
to rotaion axis). For planar_ct_1 trajectory that
should fit. As you can see at the picture, the object is moving on
a circular path but not rotating around the
center point (red cross in the image).
Kind regards,
Robert C.
*Gesendet:* Donnerstag, 12. Oktober 2017 um 07:14 Uhr
*Von:* "Simon Rit" <[email protected]
<mailto:[email protected]>>
*An:* "Robert Calliess" <[email protected]
<mailto:[email protected]>>
*Cc:* "[email protected]
<mailto:[email protected]>"
<[email protected] <mailto:[email protected]>>
*Betreff:* Re: [Rtk-users] FDK for planar ct
Hello,
No. The filter should be orthogonal to the rotation axis. The RTK
ramp filter is along the u axis of the projection.
Trajectory 2: if you take photos by rotating the cameras, they are
photographies of the same point-of-view. This is what I meant.
Cheers,
Simon
On Wed, Oct 11, 2017 at 8:58 PM, Robert Calliess
<[email protected] <mailto:[email protected]>> wrote:
Hello,
thanks for the link to the paper but I dont have access to it.
Aside from how the trajectory is interpreted within in RTK. My
actual question was
if any of those two trajectories would need another
reconstruction filter than the FDK Filter. From my point of
understanding a specific rotation around
the object is necessary for fbp/fdk (like c-arm bow, standard
circular cone-beam trajectory). That’s why I asked If the
first trajectory needs some other reconstruction
filter because the object itself doesn’t rotate around itself.
It actually gets translated on a circular path. So I was more
expecting a “yes” or “no” to the fdk filter
or a hint to another filter (except iterative reconstructions)
I should use for these trajectories.
To trajectory 2: I think the projections are different. The
object rotates and each projection shows a different view.
Kind regards,
Robert C.
*Von:*[email protected] <mailto:[email protected]>
[mailto:[email protected] <mailto:[email protected]>] *Im
Auftrag von *Simon Rit
*Gesendet:* Dienstag, 10. Oktober 2017 20:29
*An:* Robert Calliess
*Cc:* Cyril Mory; [email protected]
<mailto:[email protected]>
*Betreff:* Re: [Rtk-users] FDK for planar ct
Hi,
Let me try to clarify what I mean by "source trajectory wrt
the object." In tomography, you need to determine the source
trajectory in the object coordinate system, we don't really
care about the source trajectory in the room coordinate
system. For example, rotating the source on a circular
trajectory or rotating the object makes no difference for the
reconstruction algorithm. That's why we call diagnostic
scanners "helical scanners".
So for trajectory 1, it seems that the source trajectory
(again, wrt to the object) is a circle but the object is
offset. This is somewhat similar to
https://doi.org/10.1109/TNS.2006.880977 except that the
detector is not tilted so FDK would be the only FBP algorithm
I could think of. But the situation is really not good, data
are missing and iterative reconstruction should give better
results.
Trajectory 2: what I said in my previous email is true, it's
useless I believe, all projections are similar up to a 2D
transform of the projection.
Simon
On Tue, Oct 10, 2017 at 8:07 PM, Robert Calliess
<[email protected] <mailto:[email protected]>> wrote:
Hello,
I try to clarify the both trajectories.
Trajectory 1:
No, i dont move the source on two circles. The xray source is
fixed. Only the object and the detector moves. Both move on a
circular path so that the iso-ray
always passes through the pcb centre and the detector centre.
There is one orthogonal view and the others are the ones
moving on the circular path.
(Object is not rotating around its own axis).
Trajectory 2:
Yes, the xray source lies in the rotation axis and only the
object rotates around its z-axis. Detector and xray source are
fixed and the detector is tilted.
It’s almost like this trajectory here
https://www.ikeda-shoponline.com/engctsoft/wp-content/uploads/2016/06/Oblique-View-CT1.jpg
except that the xray source lies on the rotation axis.
I hope this helps to understand the trajectories I have to
deal with.
Kind regards,
Robert
*Von:*[email protected] <mailto:[email protected]>
[mailto:[email protected] <mailto:[email protected]>] *Im
Auftrag von *Simon Rit
*Gese**ndet:*Dienstag, 10. Oktober 2017 19:06
*An:* Robert Calließ
*Cc:* Cyril Mory; [email protected]
<mailto:[email protected]>
*Betreff:* Re: [Rtk-users] FDK for planar ct
Hi,
It's still not clear to me but what is helpful is to think in
terms of source trajectory wrt the object.
Trajectory 1: if I understand, you move the source on two
circles plus one point. I don't know of a FBP algorithm to
reconstruct this, but there might be one. I would consider
iterative reconstruction first.
Trajectory 2: your trajectory is a point, the source does not
move with respect ot the object since it lies on the rotation
axis. So each projection contains exactly the same information
up to a simple 2D projection deformation. So it's hopeless to
reconstruct from one projection only.
To create the correct geometry, I would suggest using the
function AddProjection
<https://github.com/SimonRit/RTK/blob/master/code/rtkThreeDCircularProjectionGeometry.h#L92>
for which you provide the source and detector positions plus
the 3D coordinates of the two axes of the coordinate system of
the projection.
I hope this helps
Simon
On Tue, Oct 10, 2017 at 5:43 PM, "Robert Calließ"
<[email protected] <mailto:[email protected]>> wrote:
Hello,
thank you for the fast reply.
To answer your questions first.
In this case the abbrevation pcb stands for printed circuit board.
Next point is the trajectory we are currently handling with.
Please see the attached image "trajectory.png". There are two
schematics showing the side view and top view for trajectory
type 1
and a side-view for trajectory type 2.
For type 1:
The xray source is fixed. The pcb is clamped within a
transport, so the pcb and the detector are moveable with in
the xy plane.
As you can see at the image, the pcb moves along a circular
path but the pcb itself is not rotating. And let's assume that
the iso ray
always passes through the centre of the pcb and the centre of
the detector.
For type 2:
The xray source is fixed and the detector is tilted. The pcb
lies centred in the middle of a table. So that the pcb rotates
around its centre
around the z-axis.
I hope this makes clear what trajectory i'm dealing with.
Thank you.
Kind regards,
Robert C.
*Gesendet:* Dienstag, 10. Oktober 2017 um 15:31 Uhr
*Von:* "Cyril Mory" <[email protected]
<mailto:[email protected]>>
*An:* "Robert Calliess" <[email protected]
<mailto:[email protected]>>, [email protected]
<mailto:[email protected]>
*Betreff:* Re: [Rtk-users] FDK for planar ct
Dear Robert,
Your description of the trajectory is very obscure to me.
Maybe you have a very unusual X-ray system. Could you make the
following points clear :
- what is a PCB ?
- what is fixed/moving in your system (we need this
information for the object, the source and the detector), and
what kind of trajectories have the moving parts ?
- can you re-draw your sketch with just 2 or 3 positions
(ideally, on similar but separate drawings), each one with the
object, the source and the detector ?
If you do that, we should have a clear understanding of how
your acquisition goes, and be able to give you appropriate advice.
Best regards,
Cyril
On 10/10/2017 15:02, Robert Calliess wrote:
Hello rtk users,
I have question to the RTK FDK Filter. As far as I
understand from to the fourier slice theorem the object to
be reconstructed needs a circular trajectory and needs to
rotate its own centre.
Please have a look at the attached sketch. With this
planar trajectory (Object, a PCB, is moved on a circle
trajectpry “in-plane”, PCB itself is not rotating) do I need
a special filtering if I want to use FDK for planar CT
with respect to the sketched trajectory ? I tried a
circular in-plane trajectory where the PCB is centred and
rotates
around its centre point. And with 100 projections I get
good results. But with the trajectory I described (sketch,
attached image) the results are not so good.
Because of the row-wise ramp filter It looks like there is
a directional dependency. My assumption is, and with
respect to fourier slice theorem, that the missing object
rotation (rotation around itself) causes there directional
effects.
So my questions to the experts are. Do I need to apply a
special filtering before backprojecting with FDK or is it
just the wrong
algorithm for this kind of trajectory ?
kind regards,
Robert C.
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