[Rtk-users] Reconstruction artefact with SART

[vincent]

Hi everyone,

I am trying to reconstruct a volume representing an aluminum casted part 
and investigate the differences between FDK and SART.

Here are the parameters involved: the images are 700*820 pixels and I 
have 900 projections.  The physical pixel size is 0.28 mm and the sdd 
and sid are 558.3 mm and 461.3 mm respectively, which gives me a 
magnification factor of 1.2 roughly.  I performed one iteration of SART 
with CudaRayCast as forward and backward projectors and I wanted to 
reconstruct a 700*700*700 volume with a 0.23 mm (= 0.28/1.2) voxel 
size.  The result is shown on the two pictures attached:

https://ibb.co/8sLdJxw
https://ibb.co/N3NLg2D

The result is getting worse as I increase the number of iterations

I have a hard time understanding where the stripes come from.  A 
reconstruction with the standard 256*256*256 volume and 1mm spacing 
gives a "smoother" result, closer to what FDK gives.  I thought it might 
be related to the linear system resolution, but unless I am mistaken, I 
am trying to solve a system with 700*700*700 unknown with 700*820*900 
equations, which should be ok.

Furthermore, the reconstruction with FDK at the same "full" resolution 
gives satisfactory results.

Any help/explanation will be greatly appreciated !

I thank you very much in advance,

Vincent