Forward projection for CTAC issue - help welcomed!

[kmo49]

Hello!

I am trying to forward project a three dimensional CT object to use for attenuation correction of my PET image. I am modeling 3D PET with 24 rings, maximum segment of 23. My resultant PET sinogram is 249x210x576. 210 aa bins and 249 td bins.

When I am forward projecting the CT image, the sinogram looks correct on the first slice and the last slice, but proceeds to look like stacked CT images towards the middle.

I am getting the same issue with the calculate_attenuation function. I included images below, and would appreicate any advice on how to fix this issue, thank you!