1. A method of improving the radiation detection efficiency of a time-of-flight positron emission camera having a plurality of detector rings positioned side-by-side around an area of reconstruction, each ring having a circumference and each containing a plurality of scintillation detectors which are positioned to its circumference and are pointed at the area of reconstruction to detect radiation therefrom, each detector in each ring having an opposed detector on each ring positioned 180.degree. therefrom where each detector together with an opposed detector defines a detector pair for detecting the two photons emitted within a coincidence line defined by the coincident solid angle cylindrical line connecting each detector from a positron-electron annihilation occurring in the area of reconstruction, each detector ring defining a plane slice through the area of reconstruction with an interplane slice defined as all equidistant points located between any two adjacent detector rings measured from either plane slice, and where each slice has an array of measurement positions, the method comprising the steps of: (a) determining the time-of-flight (TOF) of each annihilation detected along a coincidence line; (b) determining the position of each annihilation detected in each plane slice from the TOF of the annihilations detected along coincidence lines between detectors on the ring defining the plane slice; (c) determining from the TOF the position for each annihilation detected along each coincidence line involving detectors on different rings; and (d) forming the total detected annihilations which have occurred at each measurement position in each plane and interplane slice by (i) summing with the annihilations detected in each measurement position from coincidence lines in each plane slice the annihilations detected on coincidence lines involving detectors on different rings where the position of the annihilations so detected are within a predetermined distance of the measurement position in the plane, and (ii) summing for each measurement position on an interplane slice the annihilations detected on coincidence lines involving detectors on different rings where the position of the annihilations so detected are within a predetermined distance of the measurement position in the interplane thereby increasing the detection efficiency of the camera.