Hi Simon,
well the step size marginally improved the result. But using
CudaVoxelBased as the BP rather than CudaRayCast completely solved it !
Thank you for your time and advice,
best regards,
Vincent
On 27.10.19 21:42, Simon Rit wrote:
Hi Vincent,
I'm not sure why the step size would make such a large difference but
that's an interesting lead indeed. Feel free to add the step size as
an option, I hope this will indeed solve your problem!
Best regards,
Simon
On Fri, Oct 25, 2019 at 11:55 AM vincent <[email protected]
<mailto:[email protected]>> wrote:
Hi Simon,
thank you very much for the suggestions. I think I have a lead
and I was wondering if you could give me your opinion before I
roll up my sleeves and dive into the code.
Since the issue is number-of-voxels-dependent, and because I use
CudaRayCast both for forward and backward projections, my guess
was that it has to do with the forward projection operator, and
more specifically with the step size along the ray; while it is
an option in rtkforwardprojections, it is not customizable in
rtksart. To investigate further, I reprojected the reconstructed
FDK volume (700x700x700 voxels, voxel size = 0.23 mm) 3 times,
once with Joseph, once with CudaRayCast and the default step (1)
and one with a custom step (0.1). The vertical streaks appear as
I expected in the second case but not in the others:
https://ibb.co/ZX57FPM
https://ibb.co/MnMk5Ny
https://ibb.co/gzfPQG1
So I think that adding the step size option in rtksart should get
rid of my problem, but I would like your feedback before, as I
trust your experience more than my intuition :) !
Thanks again,
Vincent
On 23.10.19 22:30, Simon Rit wrote:
Hi Vincent,
There is a problem indeed! It's hard to guess what's the problem
from the images you sent. I would check the projections to see
what could be wrong. The first thing I would check for example is
whether air is really at 0 (as it should be). You can also look
at the difference between the forward projections of this first
iterate and the measured projections. It's known that SART should
be stopped at a few iterations but 1 should not give such a
result. You can always check if the conjugate gradient provides a
better result, you can add some regularization in it.
Good luck solving this!
Simon
On Wed, Oct 23, 2019 at 3:03 PM vincent <[email protected]
<mailto:[email protected]>> wrote:
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
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