Deadtime characteristics of anger camera

Abstract

:J) eadtime count loss may cause significant errors in quantitative measurements pcrformed by scintigraphic tcchnicJucs. In a single-crystal gamma camera it depcnds on the scattering condition, and differs among patients. In quantitative analyses of dynamic radio nuclide studies, using large activities of 9Y"'Tcflowing through organs it is ne~~ssary to determine accurately count-rate losses and to provide appropriate corrections. The dead time characteristics of Medex LF -61 Anger camera, which, consisting of a paralyzable front end and non-paralyzable display circuits, are analyzed from theoretical and experimental points of view, with consideration of the changc in the fract.ion of counts passed by the pulse height. analyzer as a function of t.he true count rat.e. The analytic methods (mathematical modeling) and the two-source met.hod were used to determine the dead time by using t.he two (104 ~lCi and 114 !--lCi)99"'Tc sources. A modified mathcmaticalmodcl (method -12) for two-componcnt systems was prcscnt.ed in t.his paper to determine the dead time. The average dead time was 9.19 !--lSecfrom t.he method -1 t.o 11 at 20% WW for 200 cm source to detect.or distance. The dead time was 4.63 !--lSecby the method -9 and it. was 4.58 ~lSec by the introduced method -12 at. 20% WW for 200 cm dist.ance. In most cases the present.ed method was found in good agreement wit.h t.he analytical and experimental results.