A MONTE-CARLO STUDY OF THE ACCEPTANCE TO SCATTERED EVENTS IN A DEPTH ENCODING PET CAMERA

We present a Monte Carlo study of the acceptance to scattered events i n a Depth Encoding Large Aperture Camera (DELAC), a hypothetical PET s canner with the capacity to encode the depth-of-interaction (DOI) of i ncident gamma-rays. The simulation is initially validated against the measured energy resolution and scatter fraction of the ECAT-953B scann er. It is then used to assess the response to scattered events in a PE T camera made of position encoding blocks of the EXACT HR PLUS type, m odified to have DOI resolution through a variation in the photopeak pu lse height. The detection efficiency for 511 keV gamma-rays, as well a s for those that scattered in the object or left only part of their en ergy in the block, is studied for several combinations of DOI sensitiv ities and block thicknesses. The scatter fraction predicted by the sim ulation for DELACs of various ring radii is compared to that of the EC AT-953B as a function of the energy threshold. The results indicate th at the poorer discrimination of object scatters with depth sensitive b locks does not lead to a dramatic increase of the scatter fraction.