[Rtk-users] how can I get a good 3d image?

[MORY, CYRIL]

Hi Erik,

Judging from the projection image you sent, you seem to be missing a crucial step.

The area around your water cylinder is white and the cylinder itself is black. This is the raw data you obtain from a scanner. It is (more or less) the power received by each
pixel of the detector. Before you backproject this, you have to convert it to attenuations.

Check out the Wikipedia page http://en.wikipedia.org/wiki/Tomographic_reconstruction.
Currently your images represent I, and you have to extract p. Only then can you hope to get something coherent from an FDK reconstruction.

Best regards,
Cyril

-----Message d'origine-----
De : rtk-users-bounces at openrtk.org [mailto:rtk-users-bounces at openrtk.org] De la part de emaddox at planet.nl
Envoyé : lundi 26 août 2013 11:48
À : rtk-users at openrtk.org
Objet : [Rtk-users] how can I get a good 3d image?

Hi,

I tried to reconstruct with RTK an example CT data set of a water phantom but so far no success.
I carefully checked all hints on the website and looked to the examples which I could  run on my system.

My data is acquired in a cone beam CT system.

My projections are tif images, 103 images each rotated by 1.98 degree steps.
The images are 640 by 512 pixels.

Distances: source to detector is 255 mm, source to centre object is 200 mm

commands I used:

rtksimulatedgeometry.exe -n 103 -a 201.96 --sdd=255 --sid=200 -o geometry.xml

rtkfdk.exe -g geometry.xml -p water -r .*.tif -o water.mha --spacing=0.169

(I tried --dimension with single slice and all slices (640))

my projections:

http://ubuntuone.com/4HZutj9lxgOZHydqBi0IM8 (30 Mb)

can someone tell me if I can (and how to) get a good reconstruction with RTK of this water phantom?

Kind regards,
Erik Maddox.
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