Development of a pixellated germanium Compton camera for nuclear medicine

Work is underway to produce a clinical imaging system, based upon the Compton camera principle, to image positron emitters. The system has been designed by computer simulation to have a spatial resolution <1 cm at the patient and have good efficiency at 511 keV. An attempt has been made to make the camera reasonably portable. The camera was constructed by ORTEC. Controlling electronics based upon GRT4 electronics boards (Daresbury, UK) are employed. The camera comprises two pixellated germanium detector planes housed 9.6 cm apart in the same vacuum housing. The scattering detector is a pixellated germanium ring with an outer diameter of 10 cm, an inner diameter of 6 cm and a thickness of 0.4 cm. A total of 152 4×4 mm² pixels are distributed in 8 blocks around the ring. The absorbing detector is a pixellated germanium cylinder with a diameter of 2.8 cm and a thickness of 1 cm. A 5×5 block of 4×4 mm² pixels are implanted in the absorbing detector. Pulse timing information and induced charge in surrounding pixels is used to improve the intrinsic spatial resolution of the detectors to an expected value of ∼1 mm. A mean energy resolution of 1.9 keV at 122 keV has been achieved, with a 0.2 keV standard deviation across the pixels. This paper will summarise the results to date and present the current state of camera developments.