[Rtk-users] Can i force the voxel values of volume be constructed to be positive?

[Simon Rit]

Hi,
I haven't implemented the ADMM algorithm but adding a constraint such as
positivity in iterative reconstruction is not a straightforward thing. The
way it's done in SART and ROOSTER is heuristic and there is no proof of
convergence. Still, you can easily add it in this way if you want to but
you'll have to modify the code. There is a wealth of literature on the
topic if you want to read it. To illustrate this complexity, you can read
the paper of Cyril Mory at the CT meeting
<http://www.ct-meeting.org/data/ProceedingsCTMeeting2014.pdf> last year.
Simon

On Thu, Aug 6, 2015 at 10:58 AM, Guangming Zang <guangming.zang at kaust.edu.sa
> wrote:

> Hi Simon,
> thanks for the explanation in detail.
> ​i can understand why​ there is only post-processing for fdk algorithm now,
> but why don't we do the non-negative  checking during each ADMM iteration?
> after all, in my opinion, in most of applications, only volume values that
> between [0,positive infinite) make sense.
> Regards
> Guangming
>
> *Guangming Zang (Alex)*
> *King Abdullah University of Science and Technology(KAUST)*
> *University of Chinese Academy of Sciences(UCAS)*
>
>
>
>
> 2015-08-06 8:27 GMT+03:00 Simon Rit <simon.rit at creatis.insa-lyon.fr>:
>
>> Hi,
>> No there is no option to force the output volume to 0. This is not the
>> same as sart where you might want to do it during the iterations. In the
>> FDK case, it's only post-processing so there is not really a reason to put
>> it in rtkfdk.
>> The nonneg option is the minimum value of the intensity that you allow
>> the Boellaard algorithm to reach after scatter correction. This does not
>> prevent negative values in the volume because the ramp filter might create
>> negative values from positive projections.
>> Simon
>>
>> On Thu, Aug 6, 2015 at 2:00 AM, Guangming Zang <
>> guangming.zang at kaust.edu.sa> wrote:
>>
>>> Dear Simon and RTK community,
>>> considering in rtksart ,we have --positivity to force the reconstructed
>>> volume values to be positive(i guess, not tested yet), i was wondering if
>>> we have any options and commands to have the same effect in algorithms fdk
>>> and admmtv since --positivity can not be found?
>>> the Boellaard scatter correction: --nonneg  is what i am looking for?
>>> Thanks in advance.
>>> Guangming
>>> *Guangming Zang (Alex)*
>>> *King Abdullah University of Science and Technology(KAUST)*
>>> *University of Chinese Academy of Sciences(UCAS)*
>>>
>>>
>>>
>>>
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>>
>>
>>
>
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