[Gate-users] inhomogeneous activity distribution in several outputfiles

[Hans-Martin Schwab]

   Hello everybody,
   for my recent simulations I wrote a script in Root that creates a
   threedimensional .raw-file storing the activity distribution as derived
   from the sourcePos information in the coincidence dataset. Observing
   that raw-file one can see irregularities in the source-distribution
   that can even be recognized in the reconstructed image of the
   simulation data. There are several artifacts, that become visible. For
   some phantoms a area of a higher number of counts is noticable in the
   x-z-plane, although a homogeneous distribution is expected. Other
   images show hot planes orientated diagonally across each subvolume. Of
   course the data stored in the sourcePos dataset does not yet contain
   corrections of sensitivity and scatter, but the shape of these areas
   with more counts can not be explained by those issues. What
   is surprising, is that when I run the same script for several times
   (where only the output name distiguishes) these irregularaties
   sometimes occur and sometimes not. Does anybody have an idea about
   that? We suppose the random generator to play a role in this (in the
   macros the Ranlux64 is used), but still we canA't really find a
   consistent idea of what might cause those artifacts.
   Best regards,
   Hans


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