Simulation studies for cylindrical positron tomography

A VMEbus-based microcomputer system has been used to implement a model for simulation of the flux of gamma rays to cylindrical PET (positron-emission-tomography) detector systems. The model is capable of tracing over one million photons per hour, and has been used to explore some of the effects of ´opening up´ planar detector geometries into volumetric imagers. Gross single-channel and coincidence rates can be estimated using the model, as well as the distribution patterns of both true and scattered coincidence events in the radial and axial directions. The model demonstrates the increases in scattered coincidences that are encountered in true (i.e. no collimation) three-dimensional PET imaging and underscores the importance of detector energy resolution in managing scattered events. The projection plane view of scattered coincidence events suggests that scatter compensation can be attempted by filtering the projection data by two-dimensional techniques. Combining this model with models of detector properties and reconstruction processes will permit a full simulation of the entire PET imaging session.