NECR analysis of 3D brain PET scanner designs

A dedicated 3D brain PET scanner has several advantages, most notably increased sensitivity, over a whole body scanner for neurological studies. However, brain scanners have higher scatter fractions, random count-rates and deadtime for the same activity concentration. We have used noise effective count-rate (NECR) analysis to compare brain scanners of 53, 60, and 66 cm diameter with the GE ADVANCE whole body scanner (93 cm diameter). Monte Carlo simulations of a brain-sized phantom (16 cm diameter, 13 cm length) in the ADVANCE geometry were used to develop a model for NECR performance, which was reconciled to results from a decay series measurement. The model was then used to predict the performance of the brain scanner designs. The brain scanners have noise effective sensitivities (the slope of the NECR curve at zero activity) as much as 40% higher than the body scanner. However, their NECR advantage diminishes quickly as the activity concentration increases. The brain scanners´ NECR equals the body scanner with about 0.7-0.8 mCi in the phantom; the body scanner has superior NECR performance at higher activity levels. An imaging center concentrating on only very low activity imaging tasks would find the efficiency advantage of a smaller detector diameter valuable, while a center performing higher activity studies such as bolus water injections or 5 mCi FDG injections might prefer the count rate performance of a whole body scanner