[Gate-users] Artifact in PET simulation output

[Jasper C]

Hello,

I've been working on the simulation of a small PET system using GATE,
and am able to obtain a .root output file from my simulation, generate
a projection file from the .root output, then use STIR to reconstruct
an image.  I have a problem in that a point source in the simulation
looks oddly distorted in the final image, and I've taken to looking at
the sinograms to find out more.

I have simulated a point source at the centre of the system, and run
another simulation with the same point source radially offset by 10 mm
from the centre. (Sinograms for the transaxial slice containing the
point source are attached - not sure if the mailing list forwards that
on.)  In both sinograms I see an odd discontinuity in the line
representing the point sources.  It happens 6 times in the sinogram,
and my detector ring is made up of 12 repeated detector blocks (ie 12
modules to a rsector).  I've also run the same simulations with a ring
made up of 16 repeated elements, and see 8 discontinuities in the
resulting lines.  That leads me to believe the artifact is related in
some way to my geometry.

I was wondering if anyone had seen something like this before and/or
could advise on what might be causing it and what I should do.

Thanks and best regards,

Jasper C.
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