Abstract: A circular array of detectors is used for detecting coincident events and the point of annihilation in a positron annihilation process in a selected plane wherein the output from the detectors is processed in a computer to provide image reconstruction for the selected plane. Bismuth germanate is shown to be more efficient than previously used detectors and the adaption of trapezoidal shape for the detectors enables more efficient utilization of the photons produced in the process. The use of absorbing metal reducing plugs between adjacent detectors may be used to decrease the aperture function of the detectors for low angles of incident radiation.

Abstract: Apparatus for determining the instantaneous occurrence of coincident pulsed signals within a selected sampling time, which apparatus stores the coincident events and which provides the required algorithmic transformation necessary to determine coincident event distribution and an interface for the utilization of a general purpose computer.