[Rtk-users] Half beam CT

[Vincent Libertiaux]

Hi Simon,

thank you for the reply and the link. I realized that I forgot the extra 
sid/sdd factor in my computation.

I wish you a pleasant day,

Vincent

On 21.02.24 10:50, Simon Rit wrote:
> 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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