[Insight-users] ring artifacts in CT

[somi]

Hi Sergio, Mario ,
Thanks for the reply. Unfortunately these images were given to me by someone
and I don't have access to scanners directly.
Median filtering seemed to suppress the noise to some extent, I would try
out Fourier analysis. I think converting the image to cylindrical
co-ordinates might help before Fourier analysis.

a) Does ITK have any frequency domain High/Low/notch etc filters ? or do I
have to create mask images depending on what type of filter I am applying ?

b) Does ITK have any Cartesian to cylindrical/spherical co-ordinate
transformation ?  Or do I have to create my own transform and pass it to
resample image filter ?

Regards,
Somi


On Wed, Apr 28, 2010 at 3:52 AM, Mario Ceresa <mrceresa at gmail.com> wrote:

> Hello Somi,
> rings artefacts happen in a CT scan if one of the detectors is faulty
> or out of calibration. The detector then gives the same erroneous
> reading at each angle and the result is a visible circle in the image.
>
> You can read about some methods to reduce them here:
>
> http://www.iop.org/EJ/article/0031-9155/54/12/018/pmb9_12_018.pdf
>
> I'm sorry but I'm not aware of any "pluggable" solution, and the
> scanner will probably need a repair/recalibration.
>
> Hope this helps,
>
> Mario
>
>
> On 28 April 2010 09:27, Sergio Vera <sergio.vera at alma3d.com> wrote:
> > It seems to me,
> > after seeing that image, my first thought is that some filtering based on
> > fourier analysis might help.
> > At least when dealing with 2D images.
> >
> > Regards
> >
> > On Tue, Apr 27, 2010 at 9:27 PM, somi <seesomi at gmail.com> wrote:
> >>
> >> Hi,
> >> I have some CT images which are severely degraded by ring artifacts
> during
> >> acquisition .
> >> The ring artifact looks something like :
> >> http://www.upstate.edu/radiology/rsna/ct/images/artifact4.jpg (not my
> image)
> >> , its more severe in my images.
> >>
> >> Has anybody encountered similar artifacts ? Is there is any out of the
> box
> >> way to remove them ?
> >>
> >> Regards,
> >> Somi
> >>
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> > --
> > Sergio Vera
> >
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