RT Journal Article SR Electronic T1 Optimizing injected activity in whole-body 3D PET: Relating NECR and singles rates JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 435P OP 435P VO 48 IS supplement 2 A1 Martin Lodge A1 Ahsan Khan A1 Arman Rahmim A1 Bruce Line A1 Frank Bengel A1 Richard Wahl YR 2007 UL http://jnm.snmjournals.org/content/48/supplement_2/435P.3.abstract AB 1806 Objectives: Whereas administered activities for 2D whole-body FDG PET studies are limited by radiation safety considerations, for 3D acquisition they are usually limited by the scanner’s count rate capability. The aim of this study was to characterize the 3D count rate capability of the GE Discovery RX with a view to optimizing whole-body FDG protocols. Methods: Noise equivalent count rate (NECR) curves were measured according to the NEMA NU 2-2001 protocol on two different scanners operating in 3D mode: GE Discovery RX (LYSO crystals) and Philips Gemini (GSO crystals). The activity concentration range on the NECR curve that corresponded to typical clinical whole body studies was determined by examining the singles rates of 75 patient studies acquired on the Gemini. The applicability of using singles rates to identify the operational range on the NECR curve was investigated over a range of count rates by calculating image signal-to-noise ratio (SNR) in a torso phantom under different conditions of padding and outside FOV activity. Results: The NECR (1R) peak was 27.8 kcps at 9.0 kBq/ml for the Gemini and 99.3 kcps at 20.5 kBq/ml for the Discovery RX. The singles rate (but not the activity concentration) at the NECR peak was consistent with that obtained at the image SNR peak for a range of phantom sizes. Patient singles rates decreased with increasing weight (mean 76.5 kg ± 19.7 kg) and were, on average, 12.6 Mcps (SD = 2.75 Mcps) following an injection of 470.2 ± 33.4 MBq FDG and mean delay of 71 min ± 21 min. These data were normally distributed so 95% confidence intervals indicate a singles range of 12.6 Mcps ± 1.96 SD. In the Gemini NECR experiment similar singles rates were obtained at an activity concentration of 3.3–9.0 kBq/ml, just below the peak of the NECR curve. Increasing the patient administration to 940 MBq (~25 mCi) would correspond to a concentration range of 6.6-18.0 kBq/ml in the NECR experiment, well below the peak of the NECR curve for the Discovery RX. Conclusions: These data suggest that for 3D whole-body FDG studies, the high count rate performance of the Discovery RX means that administered activity is limited by radiation safety factors, as opposed to scanner count rate considerations.