[Gate-users] strange counting rates

[j.hartmann at dkfz-heidelberg.de]

Hi gate users,
I have a problem with the counting rates of my simulation data.
I simulate two opposing pet heads which are rotating around the isocentre in
steps of 10 degrees. The source is a circle with a radius of 1 cm positioned at
the isocentre.
What I don`t understand are the counting rates: Although the counting rates for
each scanner position should be roughly the same because of the symmetry, I get
peaks at the angles 45 and 135. The number of detected events at these angles is
20% higher than the number at 0,90 and 180 deg.
I think there must be something wrong with my simulation setup, but I really
don`t have any idea what this could be. For the scanner rotation, I use
"orbiting" and for the source, I fixed the angle theta so that the emission
takes place only in the xy-plane, but that shouldn`t be the problem, as I have
the same peaks in the data resulting from simulations with not fixed theta. Does
anybody have an idea where the problem could be?
Cheers,
Julia