[Rtk-users] Volume error with fdkrtk backprojecting Polynomial corrected logged Projection Images.

[Steven Pollmann]

Just an update on this issue I am having.
If I just use rtkbackprojections with --method CudaBackProjection, I get 
an output volume that looks ok (obviously blurry, as no filter was 
applied).  So I target my efforts to look into the Ramp Filter.  It 
seems that this is where the issue stems from.  I have included 2 image 
screenshots.  The first (RawProjections.jpg) is a slice of the sinogram 
of the polynomial corrected projection data I would like to backproject, 
and the second (RawProjectionsRAMP.jpg) is the same data, after the RAMP 
filter has been applied (using rtkramp).  The black lines contain "NaN" 
values, and for that particular projection image, the entire image is 
turned into NaN.  So the backprojection obciously fails through those 
values.
I will do one more check to see if there are any erroneous pixels for 
the projections where the NaN occurs, but I am not confident that there 
should be any abnormal values.

Any suggestions from here?
Thanks!
Steve



On 13-08-01 11:57 AM, Steven Pollmann wrote:
> Hey RTK Users,
>
> I'm having an issue with rtkfdk output that I am trying to track down. I'm using logged projection images that have had a polynomial-based correction applied to them.  Every voxel in the output 3D mhd file (float) has a floating point value of 7FFFFFFF which, I believe is the largest 32bit float representation.  The input projection images look fine when I open them with VolView (having values ranging from -0.3(air) to 45.0 (metal screw)). The original non-corrected projections (having values ranging from -0.02(air) to 2.88(screw)) work with rtkfdk to produce a nice looking volume, so there is something I am missing.  Using in-house software, this polynomial corrected projection data reconstructs on a CPU-based implementation fine, however both CPU and CUDA backprojections from rtkfdk will not produce a valid 3d Volume for me.  If anyone has insight into what change in the projection data may cause this, that would be appreciated.  The dataset isn't proprietary (it is a scan
>   of a 4x4x4 Rubiks Cube), and so I can send files to some online storage, if needed. (It is around 2GB of projection data...).
>
> Thanks again,
> Steve
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