Hi,

I am currently trying to get started with RTK by modifying the 
FirstReconstruction example. In fact, I tried to replace the given projections 
of a sphere by some projections I created myself with Geant4. However, the 
result is not really convincing and I am not sure if I messed with the geometry 
or if I got something else wrong.


I have 90 projections (128x128 pixels, 2 deg rotation each time); from source 
to detector it's 46cm and 30cm from source to the object (simple small 
cylinder) centre, which lies in the centre of rotation:


  unsigned int numberOfProjections = 90;

  double firstAngle = 0.;

  double angularArc = 178.;

  unsigned int sid = 300.;

  unsigned int sdd = 460.;


To read in the file, I used the ITK ImageFileReader, which works well. I am 
handing in my projections stacked in .mha format because it seemed that the 
sphere projections were generated and handed to the FDK reconstruction 
algorithm in a similar way (is that correct?). My projection values are double 
type and are of a range between 0 (air) and 1.


For the FDK reconstruction I am choosing for my constant image source:

  sizeOutput.Fill(128); // output should be 3D image 128x128x128 pixels

  origin.Fill(0.); // I'm not entirely sure about this parameter? If my object 
is placed in the isocenter, this should work, right?

  spacing.Fill(0.2); // pixel length in each direction is 0.2mm


For the reconstruction itself, I didn't really change the original code but 
instead of 'rei', I handed my projections as input and then wrote the result to 
an output file.

I don't get any error when I run the program but the FDK gives some strange 
result (I am adding one screenshot of the first projection and the first slice 
of the reconstructed volume to my mail).

Maybe someone is familiar with this problem or sees what I am doing wrong? 
Thank you very much in advance!


Best regards,

Stefanie



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