Maximum likelihood positioning of scintillation events: Preliminary experiments

The centroid algorithm fails to accurately position events in slab scintillators as the location of the scintillation flash approaches the edges of the slab, an effect particularly critical in small field-of-view gamma cameras where much of the crystal is "near" an edge. Maximum likelihood (ML) positioning offers the potential of minimizing this loss by statistical estimation of event positions using detailed a priori knowledge of detector performance obtained during detector calibration. We conducted preliminary studies of ML positioning to explore two potential improvements that might (1) reduce the time to acquire high quality 2D calibration data and (2) might reduce the computational burden usually associated with ML position estimation without compromising the ability of the method to significantly increase useful field-of-view and spatial resolution. Preliminary results suggests that 2D ML positioning is indeed feasible and effective using the described calibration method combined with "row and column" readout of a detector module comprised of a multi-anode PSPMT coupled to a 44 mm square x 10 mm thick LaBr₃ slab.