Design of a three-dimensional positron camera for nuclear medicine.

A positron camera is proposed for nuclear medical imaging of radionuclide distributions in a series of isolated planes. This three-dimensional localisation is achieved through analysis of four time signals, whose differences directly measure the position (x, y, z) of individual positron annihilation events. A tetrahedronal symmetry is exploited, with two skewed plastic scintillator bars spanning a large sensitive volume. Phototubes on each end of both bars generate fast timing pulses uniquely determining the decay position through a time-of-flight technique. The mathematical properties of the transformation from the observed quantities to the spatial distribution of the radionuclide are investigated. A discussion of the efficiency of the system and the effects of Compton scattering in tissue is given. A one-dimensional pilot study encourages the development of the prototype three-dimensional positron camera.