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

[Simon Rit]

Hi,
Just a correction on Cyril's comment: there is a conversion to attenuation
with tif images, see
http://www.openrtk.org/Doxygen/classrtk_1_1TiffLookupTableImageFilter.html
It assumes that the maximum possible value is I0. You can check the result
with
rtkprojections -p. -r .*.tif -o proj.mha

I think that the problem is that you don't define the position of your
rotation center with the --proj_iso_x and --proj_iso_y options in
rtksimulatedgeometry. If you don't set those, the rotation center on the
projection image is assumed to be the point of coordinate (0,0), i.e., the
first pixel of the image with tif images. The two above-mentioned options
allow to translate this point.
Simon



On Mon, Aug 26, 2013 at 1:22 PM, MORY, CYRIL <Cyril.Mory at philips.com> wrote:

> 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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