EFFECTIVE SENSITIVITY IN 3D PET - THE IMPACT OF DETECTOR DEAD-TIME ON3D SYSTEM PERFORMANCE

3D PET has higher sensitivity than 2D PET. Sensitivity is dependant on detector properties such as density, stopping power, photofraction, e tc, but for a given detcetor material the sensitivity of a tomograph i s primarily determined by two components: the geometric solid angle fo r detection, and the fractional dead time, i.e., the time for which th e detector is unavailable for accepting events. The loss in overall se nsitivity as a function of radioactivity concentration due to these fa ctors for 3D PET has been characterised by a parameter, the effective sensitivity, which combines absolute sensitivity and noise equivalent count rates. This parameter includes scatter, system sensitivity, dead time, and random coincidence rates, and permits comparisons between d ifferent tomographs as well as the same tomograph under different cond itions. Effective sensitivity decreases most rapidly for larger, open 3D tomographs. The loss in effective sensitivity with increasing count rate suggests that new faster scintillation detectors will be needed to realize the sensitivity gain of 3D PET over a wide dynamic range of radioactivity concentrations.