Development of a time-of-flight positron imaging system

We are developing a time-of-flight (TOF) multiprobe imaging system, which is used to determine the distribution of the administered tracer substances labeled with positron emitting nuclides. A prototype system has eight detector probes, each that consists of a BaF₂ scintillator and a fast photomultiplier tube. The system construction is simple compared to positron emission tomographs by virtue of using TOF information of annihilation. We have studied the time resolution for different shapes of BaF₂ scintillators by Monte Carlo simulations and experiments, and found that truncated pyramid shaped crystals provided good time resolution with reasonable sensitivity. Coincidence time resolution of 180 to 200 ps were obtained with 16 combinations of the detectors in the system. An iterative algorithm for image reconstruction using TOF data was proposed. By introducing a proper deblurring algorithm into the image reconstruction process, the spatial resolution can be improved by a factor of two without significant amplification of noise, which corresponds to a spatial resolution of 1.5 cm