[Rtk-users] Gantry rotation direction and artefacts

[Simon Rit]

Thanks for the dataset. When I run
  rtkfdk -p . -r ^proj.mha$ -g direct.xml --spacing 0.5 -d 300 --hardware
cuda -o fdk.mha
The result looks good to me. Obviously, when I run
  rtkfdk -p . -r ^proj.mha$ -g inverse.xml --spacing 0.5 -d 300 --hardware
cuda -o fdk.mha
the result is bad since the correct rotation direction seems to be the
direct one. Did you expect the second line to produce the correct result?
Or is the first line not producing a good enough result in your opinion?


On Thu, Aug 27, 2020 at 8:21 PM Vincent Libertiaux <vl at xris.eu> wrote:

> Hi Simon,
>
> Yes, we have very decent reconstructions in the opposite direction.
>
> If you want to have a look, here is a link towards the sinogram and the
> two geometry files:
>
> https://www.dropbox.com/sh/xtzof23ar89vutm/AAASZhDBcCez_c1BN2ed74H_a?dl=0
>
> I downsampled the projections so that the file size remains reasonable.
>
> Thank you very much for you help,
> Vincent
>
> On 27.08.20 17:02, Simon Rit wrote:
>
> Hi Vincent,
> This sounds like a typical geometry problem. It's hard to guess what could
> be the problem without data. Is it a system for which you're able to
> reconstruct in the opposite direction?
> Simon
>
> On Thu, Aug 27, 2020 at 2:17 PM Vincent Libertiaux <vl at xris.eu> wrote:
>
>> Dear RTK users,
>>
>> I am trying to reconstruct a volume using the opposite rotation
>> direction; I basically defined my rotation angle to be -360 degrees and
>> my initial angle to be 359.6 (I have 900 projections).
>>
>> The results present artefacts, mostly important blurs compared to the
>> "original" reconstruction.  To be sure I was not misinterpreting the way
>> rtk deals with the geometry, I performed the same reconstruction with
>> the "direct" rotation direction (from 0 to 359.6) but reordering my
>> projections instead, which yields in the same blurry results.
>>
>> I feel I am missing some basic understanding of what is happening, any
>> help you can provide would be much appreciated !
>>
>> Best regards,
>>
>> Vincent
>>
>> _______________________________________________
>> Rtk-users mailing list
>> Rtk-users at public.kitware.com
>> https://public.kitware.com/mailman/listinfo/rtk-users
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://public.kitware.com/pipermail/rtk-users/attachments/20200827/0fa64f8f/attachment.htm>