Kinetic modeling of ¹⁸ F-PI-2620 binding in the brain using an image-derived input function with total-body PET

Accurate quantification of tau binding from ¹⁸ F-PI-2620 PET requires kinetic modeling and an input function. Here, we implemented a non-invasive Image-derived input function (IDIF) derived using the state-of-the-art total-body uEXPLORER PET/CT scanner to quantify tau binding and tracer delivery rate from ¹⁸ F-PI-2620 in the brain. Additionally, we explored the impact of scan duration on the quantification of kinetic parameters. Total-body PET dynamic data from 15 elderly participants were acquired. Time-activity curves from the grey matter regions of interest (ROIs) were fitted to the two-tissue compartmental model (2TCM) using a subject-specific IDIF derived from the descending aorta. ROI-specific kinetic parameters were estimated for different scan durations ranging from 10 to 90 minutes. Logan graphical analysis was also used to estimate the total distribution volume (V _T ). Differences in kinetic parameters were observed between ROIs, including significant reduction in tracer delivery rate (K ₁ ) in the medial temporal lobe. All kinetic parameters remained relatively stable after the 60-minute scan window across all ROIs, with K ₁ showing high stability after 30 minutes of scan duration. Excellent correlation was observed between V _T estimated using 2TCM and Logan plot analysis. This study demonstrated the utility of IDIF with total-body PET in investigating ¹⁸ F-PI-2620 kinetics in the brain.