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

[Steven Pollmann]

Hello,
I have finally been able to upload the Rubiks projections to Box.com.  It is about 2GB.  This is the link:
https://app.box.com/s/bgh5a2i3grxi6lkltrj2

In that directory, I have included a geometry file for reconstruction, and 2 linux tcsh scripts that I use to perform just a ramp filter, or a full fdk reconstruction (ZZ_doRamp.tcsh, and ZZ_doFDKRecon.tcsh).  The projections are 1024x680 floating point, but I have created a rubies_MM_Proj.mhd with the appropriate info.
I have been playing a little more with the data, and I think the issue is possibly related to the top and bottom of the projections where a collimator is partially visible (These areas do not correct well with bright- and dark-field images, as I think the collumator changes a little between acquisitions of the bright and dark fields, and the actual projections).  If I blank (set to 0.0), say the first 50 and last 50 lines, the ramp filter does not get an NaN, and is ok.  It seems the RAMP filtering function is not handling some data in these region well, possibly resulting in a divide by zero? 

I've been using this data set with RTK to test some corrections we'd like to do on the projection images...and, also, it is a pretty fun dataset to work with (4x4x4 Rubiks Cube!) 
:)
Anyhow, thanks for looking at this data.   
Steven

________________________________________
From: rtk-users-bounces at openrtk.org [rtk-users-bounces at openrtk.org] On Behalf Of MORY, CYRIL [Cyril.Mory at philips.com]
Sent: August 2, 2013 3:09 AM
To: rtk-users at openrtk.org
Subject: Re: [Rtk-users] Volume error with fdkrtk backprojecting Polynomial corrected logged Projection Images.

Hi Steve,

The problem seems to lie in the data indeed. Can you send a link to the dataset (using a Dropbox link, for example) ?

Cyril

-----Message d'origine-----
De : rtk-users-bounces at openrtk.org [mailto:rtk-users-bounces at openrtk.org] De la part de Steven Pollmann
Envoyé : jeudi 1 août 2013 22:54
À : rtk-users at openrtk.org
Objet : Re: [Rtk-users] Volume error with fdkrtk backprojecting Polynomial corrected logged Projection Images.

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
> _______________________________________________
> Rtk-users mailing list
> Rtk-users at openrtk.org
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