[Gate-users] strange counting rates

yuxuan.zhang at di.mdacc.tmc.edu yuxuan.zhang at di.mdacc.tmc.edu
Fri Mar 2 16:39:58 CET 2007

You should give the detail about your camera setup. Otherwise 
it's hard for people to figure it out what's the problem.


j.hartmann at dkfz-heidelberg.de
Sent by: gate-users-bounces at lists.healthgrid.org
03/02/2007 07:20 AM

        To:     Gate users <gate-users at lists.healthgrid.org>
        Subject:        [Gate-users] strange counting rates

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 
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 
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 
takes place only in the xy-plane, but that shouldn`t be the problem, as I 
the same peaks in the data resulting from simulations with not fixed 
theta. Does
anybody have an idea where the problem could be?

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