Time-dependant sensitivity change amendment manner null of ECT

摘要

PURPOSE:To correct secular changes in the sensitivity of an ECT apparatus efficiently, by correcting a cross calibration factor from a relationship between the total counts at the cross calibration and those at present. CONSTITUTION:As shown in the Fig. (a), a pool phantom 2 is arranged at a tunnel section 11 of a position ECT apparatus to collect data. On the other hand, as shown in the Fig. (b), a sample the same as the pool phantom 2 is put into a test tube 3 and counted with a well counter 4. A cross calibration factor is determined from a mutual relationship between the data obtained by the unit 1 and counts obtained by the well counter 4. In place of the pool phantom 2, a ring ray source is put into the tunnel section 11 to measure total counts of the ray source. Then, after a certain time elapses, the total counts are measured again. The cross calibration factor is corrected according to a relationship between the total counts thus obtained and the total counts at the cross calibration to accomplish the correction of secular changes in the sensitivity of the unit 1.