Hi,
The attached sinogram consist of line integral values, i.e., sinogram(i,j) =
-ln[ I(i,j)/I_0(i) ] where I and I_0 are the measured intensities with and
without an object, respectively.
Since we are measuring with a line detector, the “zero” (I_0) is in this case
just an array.
j is the index for the projections, i.e., j ∈ {1,2,…,360} since we take one
projection for each whole angle.
I hope this explains the sinogram and again; thank you for your time!
Best regards,
Jacob
From: [email protected] [mailto:[email protected]] On Behalf Of Simon Rit
Sent: 16. maj 2017 14:54
To: Jacob Frøsig <[email protected]>
Cc: [email protected]
Subject: Re: [Rtk-users] Reconstructing from fan-beam projections
Hi Jacob,
Thanks for the image of the sinogram. I don't understand this sinogram. Do you
know how to convert each pixel value to a line integral? I.e., if it's x-ray
imaging, do you have an image without object?
Thanks,
Simon
On Tue, May 16, 2017 at 2:24 PM, Jacob Frøsig
<[email protected]<mailto:[email protected]>> wrote:
Hi again,
and thank you for the example!
I have some trouble getting a proper reconstruction. If you have the time, any
help would be appreciated.
Attached is my fan-beam sinogram as a .tif file. Here, projections are taken
for 360 degrees and the detector has 507 pixels.
I believe the issue lies in setting the geometry and maybe the spacing between
the pixels. The measurement geometry is as follows
Source to centre: 590 mm
Source to detector: 1000 mm
Detector length: 411mm
Best regards,
Jacob
From: Rtk-users
[mailto:[email protected]<mailto:[email protected]>]
On Behalf Of Simon Rit
Sent: 15. maj 2017 17:32
To: [email protected]<mailto:[email protected]>
Subject: Re: [Rtk-users] Reconstructing from fan-beam projections
Hi,
I have added an example here:
http://wiki.openrtk.org/index.php/FanBeam
The values in the first and the third rows are not used, as illustrated in this
example. We add them to do a 2D interpolation but we do this 2D interpolation
exactly on the second row so that's not a problem.
Note that it's a bit more tricky for iterative recon but we also have a
solution for this if you need it.
Best regards,
Simon
On Mon, May 15, 2017 at 4:31 PM, Jacob Frøsig
<[email protected]<mailto:[email protected]>> wrote:
Hi again,
Thank you for the quick answer! An example would be great, thanks. I have one
concern about copying the fan-beam data:
Then we would have 2D projections for which each column is the same fan-beam
projection. By this, values of the same row are equal even though the cone-beam
geometry indicates the outer columns correspond to intensities of rays with
longer travel time through the object and hence should have attenuated more. Is
this neglectable?
Again, thanks!
Best regards,
Jacob
From: [email protected]<mailto:[email protected]>
[mailto:[email protected]<mailto:[email protected]>] On Behalf Of Simon Rit
Sent: 15. maj 2017 16:05
To: louie L <[email protected]<mailto:[email protected]>>
Cc: Jacob Frøsig <[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>
Subject: Re: [Rtk-users] Reconstructing from fan-beam projections
Hi,
I agree. What I do is do a 3 slice sinogram from the fan-beam projections by
copying the same data in each slice but reconstruct one 2D slice. If you need
an example, I can quickly demonstrate this in a short Python script.
Simon
On Mon, May 15, 2017 at 4:01 PM, louie L
<[email protected]<mailto:[email protected]>> wrote:
Hi,
I think you can carefully pad zeros to your projections. Reconstruct as if it
is a 3d object. Take the middle slice as your fanbeam result.
Let me know if it helps.
Best regards,
Louie
Sent from my iOS
Am 15.05.2017 um 15:55 schrieb Jacob Frøsig
<[email protected]<mailto:[email protected]>>:
Dear Rtk-users
I was wandering if Rtk includes an implementation of a reconstruction method to
reconstruct a 2D representation of an object given fan-beam projections.
Or, if anyone has experience using e.g. FDKConeBeamReconstructionFilter on
projections from line-detectors (fan-beam instead of cone-beam).
I hope you guys can help.
Yours sincerely
Jacob Frøsig
Project Manager
Sensor Innovation
FORCE Technology
Park Allé 345
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