New position arithmetic for scintillation camera based on floating weight system

Over the last thirty years we have been seeing impressive advances in photodetection technology and in scintillation crystal production and manufacturing. Researchers proposed an impressive variety of small FoV scintillation cameras or detector modules for SPET and PET. The original position arithmetic based on linear weight is still widely used although this logic generates a conflict between position linearity and spatial resolution. In this paper, we propose a method of position arithmetic based on floating weights, simply utilizing non linear amplification of anode charge. The method has been tested on a continuous LaBr₃:Ce scintillation crystal 51×51 mm² area and 4.0 mm thickness coupled to a Hamamatsu H8500 multi-anodes PMT. The charge collected on each anode was independently digitized, so to be free to apply to the charge distribution any different non linear transformation. In this way the charge around the peak is much more weighed then the remaining. As a result, we obtain a floating weighting matrix according to event interaction location. Comparing the data with the analogous ones from linear weights, it resulted a general improvement of more than 30% of position calibration slope and of spatial resolution values. Position linearity response and spatial resolution values resulted in good agreement with simulated ones. The best spatial resolution value was about 1.0 mm and position linearity resulted in close agreement with that of scintillation array.