A positron imaging system includes a pair of scintillation detectors for
detecting a pair of gamma rays produced by annihilation of a positron
within a distribution field, such as within a patient. An energy level
determination circuit determines the energy levels of the detected gamma
rays, and timing circuits determine whether the gamma rays have been
detected by the scintillation detectors within a predetermined time
interval. Only if the determined energy levels of each of the pair of
gamma rays meet predetermined magnitude requirements and detection of the
pair of gamma rays has occurred within the predetermined time interval,
are signals corresponding to said gamma rays inputted to processing
circuitry for calculating the spatial location of the positron. According
to a further aspect of the invention, a circuit for separating piled-up
gamma ray events includes a delay and a controllable attenuator for
delaying and simultaneously attenuating a signal outputted by the
detector, and a comparator for comparing the delayed signal with the
attenuated signal, to thereby output separate electrical pulses
representing the separate events.
