[Rtk-users] R: Trying to reconstruct with a 180 degrees circular projection geometry

[Clément Mirabel]

Hi,

Thank you both for your answer.
I managed to have a good reconstruction with 200° since my cone angle is
about 20°. I didn't mention in my original email that I was already using
Parker weightings, but as you mentioned I needed higher angles. Thank you
for your help.
As a more general question, the machine I am using to acquire data can only
rotate 180° around the patient but is still able to reconstruct (I don't
have access to the projections, it generates a 3d volume as output). Are
you aware of any algorithm that would be able to do so?

Clément

Le ven. 11 déc. 2020 à 10:03, Simon Rit <simon.rit at creatis.insa-lyon.fr> a
écrit :

> Hi Clément,
> To complement Gabriele's response and explains what goes on. FDK requires
> a 360° acquisition. RTK will calculate the angular gap between the current
> projection and the two neighbors. With your configuration, two projections
> take an angular weight (the delta when discretising the backprojection
> integral) of about 90°.
> You can do a short scan with Parker weightings but, as stated by Gabriele,
> that necessitates at least 180° + the cone angle.
> Simon
>
> On Fri, Dec 11, 2020 at 9:23 AM <gabriele.belotti.bergamo at gmail.com>
> wrote:
>
>> Hi Clément,
>>
>> It seems likely that your geometry is not 180+fan-angle complete and
>> therefore cannot lead to a proper reconstruction. From your attached
>> geometry, you sweep from 0 to 178° (180-increment).
>>
>> My suggestion would be to try some intermediate angles, so to recreate a
>> complete ShortScan. I suggest you to try at least a 200/220 ° arc to check
>> on your simulation pipeline.
>>
>> I hope this is helpful,
>> Gabriele
>>
>>
>>
>> *Da:* Rtk-users <rtk-users-bounces at public.kitware.com> *Per conto di *Clément
>> Mirabel
>> *Inviato:* venerdì 11 dicembre 2020 09:11
>> *A:* rtk-users at public.kitware.com
>> *Oggetto:* [Rtk-users] Trying to reconstruct with a 180 degrees circular
>> projection geometry
>>
>>
>>
>> Hi,
>>
>>
>>
>> I have been trying to set the geometry in
>> ThreeDCircularProjectionGeometry with values between 0 and 180 degrees, to
>> reproduce the motion of some acquisition systems, but reconstruction is far
>> from the expected result when the gantry angle does not reach max value of
>> (360-increment). (Attached is the geometry file generated)
>>
>> My workflow is the following :
>>
>>    - Apply JosephForwardProjectionImageFilter on a 3D Volume
>>    - Try to reconstruct using FDKConeBeamReconstructionFilter
>>
>> Although, the result from JosephForwardProjectionImageFilter describes a
>> 180 degrees rotation, the output of the reconstruction seems to display
>> rays from opposite direction but not from rotated directions
>>
>>
>>
>> Here is a view of what is supposed to be an axial slice:
>>
>>
>>
>> Thanks for your help!
>>
>>
>>
>> Clément
>>
>>
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>>
>
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