Analysis of interaction of gamma rays in crystals with 256ch parallel readout FP-PMT

Many incident gamma rays into crystal arrays used in PET systems are absorbed after the Compton scattering. Scattering events deteriorate detector resolutions because with common PET detectors interaction positions are calculated by Anger method and calculated positions are located at middle of an actual interaction position. If analysis of the scattering events is possible, the position resolution could be improved. A 256 channel position sensitive flat panel photo multiplier tube (256ch FP-PMT) developed by Hamamtsu Photonics is suitable for this purpose. We construct new detector which consists of a GSO crystal block and the 256ch parallel readout FP-PMT to observe aspects of gamma rays interaction in crystals event by event. The system can estimate interaction positions and deposited energies by EM algorism from anode outputs recorded individually. We performed the experiment with this detector and compared the presented method with conventional methods. In the experiment, the detector can visualize spread of scintillation light and observe the aspect of scattering events.