[Rtk-users] Half beam CT

[Simon Rit]

Hi Vincent,
This is a problem we have investigated before. Check figure 1 of this
article <https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.16869>. If
only the detector moves, it must be limited to 50% to have the center of
rotation in the beam. If both move, the motion should be limited to 50% of
the detector size times the inverse of the magnification ratio
(0.5*detsize*sid/sdd).
I guess the error message is a bit misleading?
Simon

On Tue, Feb 20, 2024 at 5:20 PM Vincent Libertiaux <vl at xris.eu> wrote:

> Hello RTK gurus,
>
> I have a question about half beam CT.  I performed a simulated CT with a
> detector displaced by half of its width and everything went smoothly.  I
> got a nice reconstruction.
> I then ran the same simulation but moved the object rather than the
> detector this time (for practical reason, it is more likely to happen in
> our real xray shots). In the rtk geometry, I imposed proj_iso_x and
> source_x to be the same value, thus modelling a displacement of the object.
>
> Unfortunately, I get a ITK ERROR: Cannot account for detector
> displacement larger than 50% of panel size.
>
> The detector displacement is the same in both cases, so I can only
> assumes the problem comes from shifting both the source and the detector ?
>
> Did I do something wrong ?
>
> Thank you in advance for any help !
>
> Best regards,
>
> Vincent
>
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