Artifacts in spiral cone-beam CT reconstruction

@AnderBiguri Hello
I tried to reconstruct the spiral cone beam CT image using an iterative reconstruction algorithm (SART, OS-SART), as I understand it only the geo.offOrigin parameter needs to be modified to synchronize the position of the bed at each angle, and the other parameters are almost unchanged, but I get the following image, which has scimitar-like artifacts in the image;
In fact, I found that it should not be a problem occurring in the projection process (Ax), it should be a problem occurring in the inverse projection process (Atb), in addition I did the same reconstruction directly using the FDK algorithm, and the result is the same as OS-SART, with the same artifacts.
the geo i used
The spiral trajectory is as follows

I also used these same geometric parameters for the sheppLogan3D simulation FDK reconstruction and the results show that the reconstructed sheppLogan image has no artifacts
the projections(two angles) is

the FDK recon image(one slice) is (there is no artifacts)

But the same geo used in real data, got the atifact results.
here is the OS-SART algorithm result（real data）
And here is the FDK result

Do you have any idea what this could be due to?

## Specifications

- MATLAB/python version: MATLAB
- OS:
- CUDA version: