Abstract
Compartmental modeling of dynamic PET data enables quantification of tracer kinetics in vivo, through the calculated model parameters. In this study the aim was to investigate the effect of early frame sampling and reconstruction method on pharmacokinetic parameters obtained from a 2-tissue model, in terms of bias and uncertainty (standard deviation, SD). Methods: The GATE Monte Carlo software was used to simulate 2×15 dynamic 18F-FLT brain PET studies, typical in terms of noise level and kinetic parameters. The data was reconstructed by both three-dimensional (3D) filtered back-projection with reprojection (3DRP) and 3D ordered subset expectation maximization (OSEM) into six dynamic image sets with different early frame durations of 1, 2, 4, 6, 10 and 15 s. Bias and SD were evaluated for fitted parameter estimates, calculated from region-of-interests. Results: The 2-tissue model parameter estimates K1, k2, and Va depended on early frame sampling, and a sampling of 6-15 s generally minimized bias and SD. The shortest sampling of 1 s yielded a 25% and 42% larger bias compared to the other schemes, for 3DRP and OSEM respectively, and a parameter uncertainty that was 10-70% higher. The schemes from 4 to 15 s were generally not significantly different in regards to bias and SD. Typically, the reconstruction method 3DRP yielded less frame sampling dependence and less uncertain results compared to OSEM, but was on average more biased. Conclusion: Of the six sampling schemes investigated in this study, an early frame duration of 6-15 s generally kept both bias and uncertainty to a minimum, for both 3DRP and OSEM reconstructions. Very short frames of 1 s should be avoided since they typically resulted in the largest parameter bias and uncertainty. Furthermore, 3DRP may be preferred over OSEM for short frames with poor statistics.