[Rtk-users] FDK for planar ct

[Cyril Mory]

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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