[Rtk-users] SART with Elekta Dataset

[Cyril Mory]

Hi Daniel,

Welcome to RTK. It's always a pleasure to have new people around.
Your problem is a frequently encountered issue with SART: your 
reconstruction volume is too small, and some of the object lies outside 
of it.

Another user recently had a similar issue, so I'll copy/paste what I 
wrote for her :
An intuitive way to understand this is the following: the algorithm 
tries to "explain" the attenuation it sees on the projections. If the 
data has been partially truncated, some rays have "extra attenuation" 
that has to go somewhere in the reconstructed volume. The center of the 
reconstructed volume is constrained by all the other rays, so this 
"extra attenuation" is pushed to the borders (or the corners). If, on 
the other hand, the reconstructed volume is large enough, this "extra 
attenuation" can go where it belongs, and does not cause hyper 
attenuation on the borders.

I've run the same command as you with spacing 2, and it gives a nice 
reconstruction result (except for the border artifacts on the bottom of 
the phantom, caused by the exact same phenomenon, which you can get rid 
of by increasing the reconstructed volume's size again). So just make 
sure your object is fully contained in the reconstructed volume, and it 
should work.

Best regards,
Cyril


On 08/14/2014 11:46 AM, Schoenke, Daniel wrote:
> Hello,
> I´ve just begun to work with RTK.
> Question: Why do I get strange results for the SART reco with the 
> Elekta dataset?
> My commands:
> rtkelektasynergygeometry --image_db ../../../elekta/elekta/IMAGE.DBF 
> --frame_db ../../../elekta/elekta/FRAME.DBF --dicom_uid 
> 1.3.46.423632.135428.1351013645.166 -o elektaGeometry
> rtksart -g elektaGeometry -p 
> ../../../elekta/elekta/img_1.3.46.423632.135428.1351013645.166/ -r 
> .*.his -o sart.elekta.mha --verbose --spacing 1 --dimension 128
> One slice of the result:
> With rtkfdk its working fine (like in the wiki).
> Can you help me please?
> Thanks.
> Daniel
>
>
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-- 
--
Cyril Mory, Post-doc
CREATIS
Leon Berard cancer treatment center
28 rue Laënnec
69373 Lyon cedex 08 FRANCE

Mobile: +33 6 69 46 73 79

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