Revision method null of the accidental coincidence in the PCT

摘要

PURPOSE:To minimize an S/N by collecting in a memory a fact that two detecting signals have been generated simultaneously, and on the other hand counting the simultaneity of a signal delayed by a prescribed time and an undelayed signal, collecting it in the second memory, performing a smoothing, and thereafter, subtracting it from the first memory. CONSTITUTION:Many radiation detectors 1, 1... are provided in a ring type in one plane, and a radiant ray radiated in the direction of 180 deg. when a positron annihilates is made incident simultaneously on two detectors 1. As a result, an output is generated from a simultaneous detecting circuit 3, and '1' is added to the contents of an address corresponding to a straight line 21 of a memory 5. On the other hand, when a gamma ray is made incident by a time difference of, for instance, 50nsc on the detectors 1, 1, respectively, an output is generated from a delay simultaneous detecting circuit 4, the contents of an address corresponding to a straight line of a memory 6 are added by '1', and counting of an off-time coincidence is executed. This counting data is brought to smoothing, and an accidental simultaneous counting data is subtracted from a simultaneous counting data. In this way, an image whose S/N is excellent can be obtained.