[Rtk-users] wrong projection geometry?

[Howard]

Hi,

I tried to run the application rtkfdk to reconstruct CBCT from 180
projections (from 0 degree to 180 degree only) that were generated using
Gate simulation. Here is the geometry of the simulation:

a cylindrical phantom (radius=8mm, height=20mm) sitting on a turntable
X-ray source to isocenter (center of the cylindrical phantom) = 80mm (SAD)
Flat panel imager (60mm x 60mm) to isocenter = 80mm (SDD=160mm)

x direction: perpendicular to y direction which is the direction from
detector to X-ray source;
z direction: turntable rotation axis and pointing upward

I used rtksimulatedgeometry application to generate the geometry xml file
following the simulation geometry with the command:
rtksimulatedgeometry -n 180 --arc 180 -o geo.xml --sid 80 -sdd 160
--proj_iso_x -30 --proj_iso_y -30

Subsequently the CBCT was reconstructed with the rtkfdk application with
the command:
rtkfdk -g geo.xml -p . -r proj.mha -o test.mha --spacing 0.1 0.1 0.2
--dimension 160,160,100 --origin -8 -8 -10

However, the reconstruction result does not look correct. Particularly the
axial and sagittal views have a lot of streaks. For your reference, I am
sharing the snapshots of the projections and the reconstructed CBCT in the
following link:

projection screenshot:         https://ibb.co/PCTjzrt
reconstruction screenshot:  https://ibb.co/QCjjvQt

What did I do wrong or miss? Or streaks are due to partial projections, ie,
only 180 views? Your help would be greatly appreciated.

Best,
Howard
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