Simulation and measurement of gamma ray and annihilation photon imaging detectors

We have developed a simulation tool that model position sensitive gamma ray and annihilation photon detectors to realistically estimate the detector performance. The simulation is based on Monte-Carlo simulation code that calculates the probability of photoelectric or Compton interaction in a given detector geometry. The propagation of scintillation light of each interaction is simulated using DETECT2000. To approximate the actual signal response of a detector, the physical geometry of each position-sensitive photon detector is modeled. The simulation is tested using position sensitive PMTs with pixellated LSO and Na(Tl) crystals. Qualitatively, the simulated and measured flood images compared very well. Both show similar edge effects and resolved the same number of crystals (21×21 for LSO and 27×27 for NaI(Tl)) compared to the "ideal" position sensitive detector resolving 22×22 for LSO and 29×29 for NaI(Tl) crystals after energy gating is applied. An intrinsic spatial integral non-linearity (INL) of 1% (for simulation) and 1.4% (for measured data before gain correction) was calculated for NaI(Tl). For LSO less than 2.3% INL is obtained in both cases (??). The linearity match is expected to improve when more accurate detector model and gain correction are applied. A finite element method is used to model with good approximation a position sensitive avalanche photodiode (PSAPD) detector surface. A third or higher order polynomial fit is applied to to an electrical Finite Element Model of PSAPD detector and provided good match with measurement, including the generation of a similar pincushion distortion pattern.