Coincidence imaging using a standard dual head gamma camera

Coincidence electronics and a data acquisition system were developed to explore coincidence detection using a conventional dual head gamma camera. A high impedance pick-off circuit provides position and energy signals without interfering with normal camera operation. The signals are pulse-clipped to reduce pileup effects. Thin lead-tin-copper filters are used to reduce the flux of low energy photons to the detectors. The data are stored in list mode format. The measured coincidence timing resolution for the system is 9 nsec FWHM (450 kcps/detector) and the energy resolution is 11% (650 kcps/detector). The system sensitivity is 46 kcps/μCi/cc for a 20 cm diameter (18 cm length) cylindrical phantom centered in the field of view. A scatter fraction of 31% was measured using the 20 cm cylindrical phantom. The sensitivity and scatter fraction measurements were made using a 450-575 keV energy window, 63.0 cm detector spacing, and 1 mm thick lead filters. The maximum recommended singles rate (full spectrum) for coincidence imaging is ∼800 kcps per detector. The 3D reprojection algorithm has been implemented. Example images of the 3D Hoffman brain phantom and patient tumor images are shown