Optimization of the injected activity in dynamic 3D PET: A generalized approach using patient-specific NECs as demonstrated by a series of 15O-H2O scans

The magnitude of the injected activity (A0) has a direct impact on the statistical quality of PET images. This study aimed to develop a generalized method for maximizing the statistical quality of dynamic PET images by optimizing A0. Methods: Patient-specific noise-equivalent counts (PS-NECs) were used as a metric of the statistical quality of each time frame of a dynamic PET image. Previous methodology developed to extrapolate the NEC as a function of A0 was extended to dynamic PET, enabling the NEC to be extrapolated as a function of both A0 and the time after injection. This method allowed A0 to be optimized after a single scan (at a single A0), by maximizing the NEC within the time interval for which the parameter estimation is most sensitive. The extrapolation method was validated by a series of 15O-H0O scans of the body acquired in 3-dimensional mode. Each patient (n = 6) underwent between 3 and 6 scans at 1 bed position. The injected activities were varied over a wide range (140-840 MBq). Noise-equivalent counting rate (NECR) versus A0 curves and the optimal injected activities were calculated from each injection. Results: PS-NECR versus A0 curves as extrapolated from different injected activities were consistent (coefficient of variation, typically