Figures of Merit for Different Detector (Configurations Utilized in High Resolution Positron Cameras

A new positron camera system is currently being designed by our group. The goal is an instrument that can measure the whole brain with a spatial resolution of 5 mm FWHM in all directions. In addition to the high spatial resolution, the system must be able to handle count rates of 0.5 MHz or more in order to perform accurate fast dynamic function studies such as the determination of cerebral blood flow and cerebral oxygen consumption following a rapid bolus. An overall spatial resolution of 5 mm requires crystal dimensions of 6*6*L mm3, or less, L being the length of the crystal. Timing and energy requirements necessitate high performance photomultipliers. The identification of the small size scintillator crystals can currently only be handled in schemes based on the Anger technique, in the future possibly with photodiodes. In the present work different crystal identification schemes have been investigated. The investigations have involved efficiency measurements of different scintillators, line spread function studies and the evaluation of different coding schemes in order to identify small crystals.