Hi Sergio, Mario ,<br>Thanks for the reply. Unfortunately these images were given to me by someone and I don't have access to scanners directly.<br>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.<br>
<br>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 ?<br><br>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 ?<br>
<br>Regards,<br>Somi<br><br><br><div class="gmail_quote">On Wed, Apr 28, 2010 at 3:52 AM, Mario Ceresa <span dir="ltr"><<a href="mailto:mrceresa@gmail.com">mrceresa@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="im">Hello Somi,<br>
rings artefacts happen in a CT scan if one of the detectors is faulty<br>
or out of calibration. The detector then gives the same erroneous<br>
reading at each angle and the result is a visible circle in the image.<br>
<br>
You can read about some methods to reduce them here:<br>
<br>
<a href="http://www.iop.org/EJ/article/0031-9155/54/12/018/pmb9_12_018.pdf" target="_blank">http://www.iop.org/EJ/article/0031-9155/54/12/018/pmb9_12_018.pdf</a><br>
<br>
I'm sorry but I'm not aware of any "pluggable" solution, and the<br>
scanner will probably need a repair/recalibration.<br>
<br>
Hope this helps,<br>
<br>
Mario<br>
<br>
<br>
On 28 April 2010 09:27, Sergio Vera <<a href="mailto:sergio.vera@alma3d.com">sergio.vera@alma3d.com</a>> wrote:<br>
</div><div><div></div><div class="h5">> It seems to me,<br>
> after seeing that image, my first thought is that some filtering based on<br>
> fourier analysis might help.<br>
> At least when dealing with 2D images.<br>
><br>
> Regards<br>
><br>
> On Tue, Apr 27, 2010 at 9:27 PM, somi <<a href="mailto:seesomi@gmail.com">seesomi@gmail.com</a>> wrote:<br>
>><br>
>> Hi,<br>
>> I have some CT images which are severely degraded by ring artifacts during<br>
>> acquisition .<br>
>> The ring artifact looks something like :<br>
>> <a href="http://www.upstate.edu/radiology/rsna/ct/images/artifact4.jpg" target="_blank">http://www.upstate.edu/radiology/rsna/ct/images/artifact4.jpg</a> (not my image)<br>
>> , its more severe in my images.<br>
>><br>
>> Has anybody encountered similar artifacts ? Is there is any out of the box<br>
>> way to remove them ?<br>
>><br>
>> Regards,<br>
>> Somi<br>
>><br>
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><br>
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