Physical evaluation of 511 keV imaging with gamma camera and PET

This work presents an evaluation of a gamma camera operating in coincidence mode. The major limitations of these cameras compared to full-ring PET are the limited count rate and sensitivity. The authors evaluate the progress in count rate which was made by upgrading the system with new electronics. At the moment most gamma cameras use septa to limit the axial acceptance angle for coincidences. Sensitivity can be improved by removing the septa, which results in a fully 3D acquisition. The improvements in sensitivity are measured. Another limitation is the non-uniform sensitivity due to the varying acceptance angle, which decreases linearly from the center towards the edges in a 180° opposed dual head configuration. Sensitivity and uniformity can be improved by going from a dual head to a triple head configuration. As triple head coincidence is not yet available, the authors calculated the theoretical sensitivity profiles from geometrical considerations