"Positology"-the search for suitable detector arrangements for a positron ECT with continuous rotation

This paper proposes a continuously rotating positron ECT system, in which the detectors are arranged on a circular ring with "non-uniform" spacing so as to provide much finer sampling interval in the projections than the conventional circular ring system. The address signals on the coincidence events are read out through a rotary photo-coupler, and the detector system can be rotated at a desired speed. Suitable detector arrangements are searched which provide sufficiently fine sampling interval with reasonable sampling density uniformity. Assuming about 50 detectors are arranged on a circle, the sampling characteristics of various detector arrangements have been examined. An iterative search method has also been applied to find a reasonable arrangement. The best arrangement has been obtained by the iterative method. It has an effective sampling interval of the order of (1/200)R, where R is the radius of the detector array, and the sampling density uniformity after 5-point smoothing is -7.8 ˜/spl I.chemo/18 % in the range of /spl I.chemo/ R/2.