NOISE EQUIVALENT COUNT MEASUREMENTS IN A NEURO-PET SCANNER WITH RETRACTABLE SEPTA

Removal of interplane septa in a PET scanner enables acquisition of all possible lines of response (3-D mode) in an effort to maximize the available number of detected events. One problem with this method at high count rates, however, is a markedly increased deadtime and randoms rate, which has a deleterious effect on data quality. The noise-equivalent count-rate (NEC) performance of a neuro-PET scanner has been determined with and without interplane septa on uniform cylindrical phantoms of differing radii and in human studies to assess the optimum count rate conditions that realise the maximum gain. In the brain, the effective gain in NEC performance for 3-D ranges from > 5 at low count rates to almost-equal-to 3.3 at 200 kcps (equivalent to 37 kcps in 2-D). The gains of the 3-D method assessed by this analysis are significant, and are shown to be highly dependent on count rate and object dimensions.