Effect of the distribution of radioactive sources on deadtime loss in a single-crystal gamma camera.

Quantitative studies with a single-crystal gamma camera often require correction for deadtime count loss. We evaluated the deadtime characteristics of a gamma camera using point sources. Point sources with various radioactivities were measured, and the relation between radioactivity and count rate was assessed. Two sources with different activities were imaged apart or adjacent to each other, and the effect of the geometrical distribution on counting efficiency was investigated. Count loss was increased at a high radioactivity level, and was well corrected using a nonparalyzable model and a deadtime of 4.99 microsec. It was not affected by the distance between the two sources, and occurred equally for the two sources imaged together. The count loss in imaging two sources was successfully corrected by multiplying the obtained image by a correction factor based on the count rate in the whole field-of-view. These results support the reliability of the analytic technique for deadtime correction.