[Rtk-users] Error message: cannot account for detector displacement larger than 50% of panel size

[Simon Rit]

Hi Vincent,
This generally occurs when your detector offset is not adequately passed to
the geometry. When you say that you have "5.2mm and -8mm" offsets, I guess
it is with respect to a centered geometry, where the central ray hits the
detector. For this to be the case in RTK, you must check that the
coordinate (0,0) mm corresponds to the center of the detector. By default,
I guess that tif puts it in the corner. So you probably need to add to
rtkprojections an option like --neworigin xorig,yorig,0 where xorig and
yorig is something like -0.5*(npixels-1)*spacing.
If that doesn't help, you don't need to share the data, the mhd headers are
sufficient to test the geometry.
Good luck!
Simon

On Mon, Oct 1, 2018 at 5:13 PM vincent <vl at xris.eu> wrote:

> Hi everyone,
>
> I am facing a problem when I try to reconstruct an object. I'll try to
> be as complete as possible in the description.
>
> I acquired 18000 views from a custom-made ct scanner, of which I
> extracted 360 for the sake of reconstruction speed for my tests. The
> images are cropped to 1001*1761 pixels.  An external calibration program
> estimated that the x and y detector offsets where 5.2mm and -8mm
> respectively.  The sdd and sid are 983mm and 483mm.  I used those value
> to generate a simulated geometry.
>
> I then created a projection volume with the command
>
> rtkprojections -v  -o rec1Proj.mha -p . -r cropped.*.tif --i0 7000 where
> I estimated the i0 value on the images background (for the sake of
> completeness, I also tested with the automatic value which resulted in
> the same problem)
>
> Finally, I wanted to reconstruct the volume with the command
>
> rtkfdk  -g geoCT.xml -p . -r rec1Proj.mha  --spacing 0.2 --dimension
> 1761,1761,1761 -v -o recFDK.mha  --hardware cuda
>
>
> The exact error message is:
>
> Reconstructing and writing... ExceptionObject caught with
> writer->Update() in file
> ~/IPTools/RTK/RTK/applications/rtkfdk/rtkfdk.cxx line 218
>
> itk::ExceptionObject (0x1cf4b90)
> Location: "unknown"
> File: ~/IPTools/RTK/RTK/code/rtkDisplacedDetectorImageFilter.hxx
> Line: 155
> Description: itk::ERROR: Cannot account for detector displacement larger
> than 50% of panel size. Corner inf=2.55504 and corner sup=100.826
>
> I had a look at the aforementionned line in the
> rtkDisplacedDetectorImageFilter.hxx file but I didn't really understand
> how the corners are computed in the
> inputPtr->TransformIndexToPhysicalPoint(inputPtr->GetLargestPossibleRegion().GetIndex(),
>
> corner function.
>
> I have no problem sharing the projections if needed, but they weight 1.3
> Go altogether.
>
>
> I thank you very much in advance for any kind of help you can provide.
>
> Best regards,
>
> Vincent
>
>
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