[Rtk-users] Parker short scan test for enough over scan

[Chao Wu]

Hi Fredrik,

It is because the "halfDetectorWidth" here is the value for an untilted
virtual detector at the isocenter which is equivalant to the real detector.

Regards,
Chao

2017-09-25 14:01 GMT+02:00 Fredrik Hellman <fredrik.hellman at gmail.com>:

> Hi,
>
> In rtkParkerShortScanFilter.hxx (line 113) and
> rtkCudaParkerShortScanFilter.cxx (line 95), the overscan angle is checked
> to be large enough for the used beam fan angle. (There is a difference
> between how this check is performed in the two cases. It seems like the
> CUDA-version assumes that the piercing point is in the middle of the
> detector. That's not what this question is about though.)
>
> The beam fan angle seems to be computed as
>
> arctan( halfDetectorWidth / sourceToIsocenterDistance )
>
> Why sourceToIsocenterDistance? Shouldn't it be sourceToDetectorDistance?
> If the detector is far away from the isocenter, the beam fan angle should
> also be small as far as I understand. This is not reflected in this
> computation.
>
> Best regards,
> Fredrik Hellman
>
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