Preliminary Study of a Germanium Three-Dimensional Camera for Positron Emitting Radioisotopes

A preliminary feasability study of a camera for imaging of positron emitting radioisotopes based on two arrays of Ge detectors operated in coincidence has been carried out. Efficiency, effects of energy resolution, and timing characteristics have been studied. It has been found that Ge can compete favorably with NaI in efficiency if Compton signals can be admitted for imaging. Analysis of the effect of scattered radiation indicates the advisability of having some moderate energy resolution in the system. A method is devised which allows the use of the Compton signals of the Ge detectors in a summing mode and, therefore, maintain very good energy resolution. A study of the timing properties of small Ge detectors indicates that count rates as high as one order of magnitude more than those possible with NaI detector arrays should be possible. Also, for the first time, it appears realistically possible that tomography by time-of-flight techniques can be carried out with a camera. It is concluded that a small prototype camera section should be built and investigated further.