One Year Experience with a High Resolution Ring Detector Positron Camera System: Present Status and Future Plans

A ring detector positron camera system for brain research is described. The system utilizes 95 8 × 20 × 50 mm NaI (T1) detectors and is simultaneously recording coincidences from 1900 detection channels over a 30 cm diameter image field. To improve sampling two motions of the detector ring are utilized: a small rotation of half a crystal distance combined with a wobbling motion. The time window of the detection channels for accepting coincidences is 22 ns. Each detection channel corresponds to a unique address which labels any recorded event. Before being temporary stored in a buffer memory the event address passes through a PROM module which 1) removes events outside the specified image field and, 2) rearranges the event address to a projection address, i. e. a hard ware preprocessing of incoming data. The effective intrinsic resolution is 5.5 mm at the center of the image field and, together with a four point wobble, an overall resolution of 7 mm is obtained. The sensitivity is 5500 c/s for a 20 cm diameter cylinder containing 1 μCi/cc of a uniformly distributed positron activity in water. The system has been in clinical use since June 1978.