[Rtk-users] bright circle on the reconstructed image

[Howard]

Thanks very much, Cyril & Simon. Now the fdk reconstruction is working
beautifully. Jus another quick question: for rtksart executable, are we
still able to do padding and hanning window trick as well?

On Thu, Sep 18, 2014 at 9:47 AM, Simon Rit <simon.rit at creatis.insa-lyon.fr>
wrote:

> Hi,
> I fully agree with Cyril. Something else : you might want to mask out what
> is outside the field-of-view using the rtkfieldofview executable. Your ring
> corresponds to that border. See an example here:
> http://wiki.openrtk.org/index.php/RTK/Examples/VarianReconstruction
> Simon
>
> On Thu, Sep 18, 2014 at 10:12 AM, Cyril Mory <
> cyril.mory at creatis.insa-lyon.fr> wrote:
>
>>  Hi Howard,
>>
>> The bright ring artifact is typically caused by high-pass filtering (the
>> ramp filter used in FDK) of truncated projection data (when projections
>> have non-zero values on the sides, the edge of the projection makes a sharp
>> transition to zero). A classical answer to this problem is to pad the
>> projections, for example with values starting from the values on the side
>> and slowly decreasing to zero.
>>
>> rtkfdk can do this padding for you. Just add "--pad 0.1" to your options
>> (or more than 0.1 if it isn't enough).
>> Also, I noticed that your reconstructed image seems quite noisy. You
>> might want to use a Hann windowing of the ramp filter to reduce the noise
>> amplification effect of high-pass filtering. You can do that by adding
>> "--hann 0.5" to your options. Note that the argument is a cut-off
>> frequency, so smaller values mean more smoothing.
>>
>> Best regards,
>> Cyril
>>
>>
>> On 09/18/2014 05:21 AM, Howard wrote:
>>
>>  Hi,
>>
>> I use rtkfdk to reconstruct varian cbct images following the example on
>> rtk wiki page. The projections were obtained with half fan mode because it
>> is an abdominal region with the patient lateral x AP dimension of 550x550.
>> The reconstructed cbct images have a big bright circle around
>> the image. Please see the image:
>> http://expirebox.com/download/2f55c9d8f0bc83138b954d2fec08e78c.html
>>
>> I am using Ubuntu Linux box to reconstruct. Two sequential commands were
>> used:
>>
>> ./rtkvarianobigeometry --xml_file ProjectionInfo.xml --path Scan0/
>> --regexp Proj_.*.hnd -o varianGeometry
>>  and
>>
>> rtkfdk \
>>    --geometry varianGeometry \
>>    --regexp .*.hnd \
>>    --path ../Scan0 \
>>    --output rec.mha \
>>    --verbose \
>>    --spacing 2.0,2.0,2.0 \
>>    --dimension 256,100,256 \
>>  The projections are stored in the standard varian format: Scan0 and
>> ProjectionInfo.xml with 644 projection images.  I assume that rtkfdk
>> handled the half fan geometry properly. What did I do wrong then?  Many
>> thanks!
>>
>> -howard
>>
>>
>> _______________________________________________
>> Rtk-users mailing listRtk-users at public.kitware.comhttp://public.kitware.com/mailman/listinfo/rtk-users
>>
>>
>> --
>> --
>> 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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>>
>>
>
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