[Rtk-users] wrong projection geometry?

[Howard]

Hi Simon,

I did run a full acquisition but with less projection views and it turned
out that the streaks were due to short angles, ie, 180 degree is not
sufficient. Thanks for your reply.

Howard

On Thu, Aug 1, 2019 at 10:42 PM Simon Rit <simon.rit at creatis.insa-lyon.fr>
wrote:

> Hi,
> From what I see in your reconstruction screenshot, you have mainly one
> projection. 180° is too short for a short scan so I suggest to have at
> least 180°+cone angle. Don't you get a warning when launching the command
> line? It's hard to anticipate what happens if you don't use this amount of
> data.
> Since it's a Gate simulation, I suggest to start with a full acquisition
> to check that everything else is correct (distances, rotation direction,
> etc).
> Don't hesitate to share your Gate macro if you want us to check the
> geometry.
> Note that your spacing and origin parameters need commas instead of spaces
> or quotes to be adequately interpreted
> Simon
>
> On Sun, Jul 28, 2019 at 5:15 PM Howard <lomahu at gmail.com> wrote:
>
>> Hi,
>>
>> I tried to run the application rtkfdk to reconstruct CBCT from 180
>> projections (from 0 degree to 180 degree only) that were generated using
>> Gate simulation. Here is the geometry of the simulation:
>>
>> a cylindrical phantom (radius=8mm, height=20mm) sitting on a turntable
>> X-ray source to isocenter (center of the cylindrical phantom) = 80mm (SAD)
>> Flat panel imager (60mm x 60mm) to isocenter = 80mm (SDD=160mm)
>>
>> x direction: perpendicular to y direction which is the direction from
>> detector to X-ray source;
>> z direction: turntable rotation axis and pointing upward
>>
>> I used rtksimulatedgeometry application to generate the geometry xml file
>> following the simulation geometry with the command:
>> rtksimulatedgeometry -n 180 --arc 180 -o geo.xml --sid 80 -sdd 160
>> --proj_iso_x -30 --proj_iso_y -30
>>
>> Subsequently the CBCT was reconstructed with the rtkfdk application with
>> the command:
>> rtkfdk -g geo.xml -p . -r proj.mha -o test.mha --spacing 0.1 0.1 0.2
>> --dimension 160,160,100 --origin -8 -8 -10
>>
>> However, the reconstruction result does not look correct. Particularly
>> the axial and sagittal views have a lot of streaks. For your reference, I
>> am sharing the snapshots of the projections and the reconstructed CBCT in
>> the following link:
>>
>> projection screenshot:         https://ibb.co/PCTjzrt
>> reconstruction screenshot:  https://ibb.co/QCjjvQt
>>
>> What did I do wrong or miss? Or streaks are due to partial projections,
>> ie, only 180 views? Your help would be greatly appreciated.
>>
>> Best,
>> Howard
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>
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